Free C-36 Practice Questions: Underground and Rough Systems
60 free questions with answers, explanations and the official source for each. Answer one to see why. No sign-up.
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1 / 60
A building sewer has passed inspection. Under CPC 314.4, how must the trenches be backfilled over the piping?
CPC 314.4 requires excavations to be completely backfilled as soon after inspection as practicable, with trenches backfilled in thin layers to 12 inches above the top of the piping with clean earth free of stones, boulders, and debris. Mechanical equipment may then complete the backfill to grade.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 314.4
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A proposed building is on a lot that abuts a public sewer. Under CPC Section 713.4, the public sewer may be treated as unavailable when it lies beyond what distance from the proposed building?
CPC Section 713.4: the public sewer may be considered as not being available where it is located more than 200 feet from a proposed building on a lot that abuts and is served by it.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 713.4
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A crew has laid pipe in a 6 foot deep shored trench in Type B soil. Under Title 8 Section 1541.1, how must the support systems come out?
Title 8 Section 1541.1 requires removal of support systems to begin at, and progress from, the bottom of the excavation, with members released slowly to watch for failure or cave-in, and backfilling to progress together with the removal.
Source: Cal/OSHA Construction Safety Orders (CCR Title 8, Subchapter 4) T8 1541.1
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A horizontal drain is installed rising away from the point of disposal at 0.5 percent. Does it meet CPC 708.1?
CPC 708.1 requires horizontal drainage piping at a uniform slope of not less than 1/4 inch per foot or 2 percent toward the point of disposal. A pipe that rises away from the point of disposal does not meet that.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 708.1
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How does the CPC define a private sewage disposal system?
CPC 202.1 defines a private sewage disposal system as a septic tank with the effluent discharging into a subsurface disposal field, into one or more seepage pits, or into a combination of the two, or other facilities permitted elsewhere in the code.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 202.1
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What is the primary purpose of the vent system in DWV piping?
CPC 901.2 requires each plumbing fixture trap to be protected against siphonage and backpressure, with air circulation ensured throughout the drainage system by vent pipes. Under CPC 901.3 the vent system keeps a trap seal from a pressure differential exceeding 1 inch water column.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 901.2
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Under CPC Table 702.1, what is the minimum trap and trap arm size for a lavatory?
CPC Table 702.1 lists the minimum trap and trap arm size for a lavatory as 1 1/4 inches.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 702.1
8 / 60
A crew tunnels under a driveway between two open-cut trenches that are 20 feet deep. Under CPC Section 314.2, what is the maximum length of the tunnel?
CPC Section 314.2: tunnels shall be limited in length to one-half the depth of the trench, with a maximum length of 8 feet. One-half of 20 feet is 10 feet, so the 8 foot maximum governs.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 314.2
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During a bathroom remodel, a plumber wants to make the lavatory's waste connection to the side of the water closet's closet bend. Under CPC Section 310.3, is this allowed?
CPC Section 310.3: no waste connection shall be made to a closet bend or stub of a water closet or similar fixture.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 310.3
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Heavy rain leaves accumulated water 2 feet deep in a 4 foot deep trench. Under Cal/OSHA Title 8 Section 1541, may employees work in it?
Title 8 Section 1541(h) says employees shall not work in excavations with accumulated water unless adequate precautions have been taken, which could include special support or shield systems, water removal, or a safety harness and lifeline. If water removal equipment is used, a competent person must monitor it.
Source: Cal/OSHA Construction Safety Orders (CCR Title 8, Subchapter 4) T8 1541
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A water supply pressure test shows a drop from 100 psi to 99 psi over 30 minutes. What is the result?
CPC 609.4: the system must withstand the test pressure without evidence of leakage for at least 15 minutes. A steady drop means a leak; find it, repair it, and retest.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 609.4
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A lavatory's 1 1/4 inch trap arm runs 15 feet (180 inches) to the nearest vent. Under CPC Table 1002.2, what is the problem?
CPC Table 1002.2 allows a 1 1/4 inch trap arm at most 30 inches from the trap weir to the vent. At 180 inches this trap arm is far too long.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 1002.2
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A CSST system will carry gas at a pressure in excess of 14 inches water column. Under CPC Section 1213.3, what pressure test is required?
CPC Section 1213.3: for CSST carrying gas at pressures in excess of 14 inches water column, the test pressure shall be not less than 30 psi for 30 minutes.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1213.3
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Under CPC 408.5, what is the minimum diameter of a shower's waste outlet and fixture tailpiece?
CPC 408.5 requires showers to have a waste outlet and fixture tailpiece not less than 2 inches in diameter.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 408.5
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Under CPC Table 702.1, what are the minimum trap and trap arm sizes for a bathtub and for a domestic kitchen sink?
CPC Table 702.1 lists a 1 1/2 inch minimum trap and trap arm for both a bathtub or combination bath/shower and a domestic kitchen sink. A lavatory is smaller, at 1 1/4 inches.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 702.1
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Under Title 8 Section 1541, what must a competent person do for an open trench?
Title 8 Section 1541 requires a competent person to make daily inspections of excavations, the adjacent areas, and protective systems for signs of possible cave-ins, failing protective systems, hazardous atmospheres, or other hazards. The inspection is done before work starts, as needed during the shift, and after every rain storm or other hazard increasing occurrence.
Source: Cal/OSHA Construction Safety Orders (CCR Title 8, Subchapter 4) T8 1541
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Under CPC 105.2, when is the rough-in inspection made?
CPC 105.2 requires the rough-in inspection to be made prior to the installation of wall or ceiling membranes. The underground inspection is made before backfill is put in place, and the final inspection upon completion of the installation.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 105.2
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Under the CPC, how are leaks located in fuel gas piping under test pressure?
CPC 1213.4.1 requires leakage to be located by means of an approved gas detector, a noncorrosive leak detection fluid, or other approved leak detection methods. CPC 1213.1.6 says oxygen shall not be used as a test medium.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1213.4.1
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An island sink trap is vented with a returned vent under the counter. Under CPC Section 909.1, how high must the vent rise before it returns downward?
CPC Section 909.1: traps for island sinks may be vented by extending the vent as high as possible, but not less than the drainboard height, and then returning it downward to the horizontal sink drain.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 909.1
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Under CPC 105.2.1, when may plumbing piping be covered or concealed?
CPC 105.2.1 requires work that is covered or concealed before being inspected, tested, and approved to be uncovered for inspection. CPC 105.2.1.1 says no water supply system shall be covered or concealed until it has been tested, inspected, and approved.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 105.2.1
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Under CPC 1401.1, which piping penetrations must be protected?
CPC 1401.1 requires piping penetrations of required fire-resistance-rated walls, partitions, floors, floor/ceiling assemblies, roof/ceiling assemblies, or shaft enclosures to be protected in accordance with the building code and that chapter.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1401.1
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Under CPC Section 1212.9, which of these appliances is exempt from the sediment trap requirement?
CPC Section 1212.9: illuminating appliances, gas ranges, clothes dryers, decorative appliances for vented fireplaces, gas fireplaces, and outdoor cooking appliances are not required to have a sediment trap.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1212.9
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A plumber installs a 3/4 inch PEX water supply line. Under CPC Table 313.3, what is the maximum horizontal support spacing?
CPC 313.3 requires suspended piping to be supported at intervals not exceeding Table 313.3, which lists PEX 1 inch and smaller at 32 inches horizontally and 1 1/4 inches and larger at 4 feet. Copper 1 1/2 inches and smaller is 6 feet.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 313.3
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A horizontal building drain carries a total load of 145 DFU at 1/4 inch per foot. Starting at 3 inch and going up, which is the first pipe size in Table 703.2 that can carry that load?
Table 703.2: a 3-inch horizontal drain carries a maximum of 35 fixture units and a 4-inch a maximum of 216. 145 is more than 35 and within 216, so 4 inch is the first size that works.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 703.2 (cells)
25 / 60
A public restroom has four lavatories, two 1.6 gpf flushometer-valve water closets, and two 1.0 gpf integral-trap urinals. Using CPC Table 702.1 public values, what is the total DFU load?
Table 702.1 public column: lavatory 1.0, water closet 1.6 gpf flushometer valve 4.0, urinal integral trap 1.0 gpf 2.0. Total 4 x 1 + 2 x 4 + 2 x 2 = 16 DFU.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 702.1
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A gas line is being installed to a furnace. At what point should the shutoff valve be located?
CPC 1212.6: each appliance has its own accessible manual shutoff valve serving that appliance only, located within 6 feet of the appliance, upstream of the connector where one is used.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1212.6
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Under Title 8 Section 1541.1(a), when may an excavation go without a protective system (shoring, sloping, or a shield)?
Title 8 Section 1541.1(a) requires each employee in an excavation to be protected from cave-ins by an adequate protective system, except where the excavation is made entirely in stable rock, or is less than 5 feet in depth and a competent person's examination of the ground shows no indication of a potential cave-in.
Source: Cal/OSHA Construction Safety Orders (CCR Title 8, Subchapter 4) T8 1541.1
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Under CPC 708.1, what is the minimum slope for 3 inch horizontal drainage piping?
CPC 708.1: horizontal drainage piping slopes at not less than 1/4 inch per foot. Only a building drain 4 inches or larger may drop to 1/8 inch per foot, where 1/4 is impractical and the AHJ approves it first.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 708.1
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A building sewer built of materials approved for use inside a building passes near a domestic water supply well. Under the notes to CPC Table 721.1, what is the minimum horizontal distance to the well?
Notes to CPC Table 721.1: drainage piping shall clear domestic water supply wells by not less than 50 feet, reduced to not less than 25 feet where the drainage piping is constructed of materials approved for use within a building.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 721.1
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A wall-hung urinal is installed on the third floor of an office building. Under CPC Section 707.4, what cleanout is required for it?
CPC Section 707.4: a cleanout shall be installed above the fixture connection fitting serving each urinal, regardless of the location of the urinal in the building.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 707.4
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A horizontal drain line 4 feet long serves a kitchen sink. Under CPC Section 707.4, may its cleanout be omitted?
CPC Section 707.4: cleanouts may be omitted on a horizontal drain line less than 5 feet in length unless the line is serving sinks or urinals. This line serves a kitchen sink, so the cleanout is required.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 707.4
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A plumbing contractor gets an 811 ticket before trenching for a sewer lateral. Under Government Code Section 4216.2, how long is the ticket valid?
Government Code Section 4216.2: a ticket shall be valid for 28 days from the date of issuance. If work continues beyond 28 days, the excavator must renew the ticket.
Source: Government Code 4216 to 4216.24 (Underground Service Alert: excavation and 811) GOV 4216.2
33 / 60
A 6-inch building sewer runs 120 feet. The AHJ has approved the reduced slope allowed by the CPC 718.1 exception. What is the minimum total drop?
CPC 718.1: building sewers slope at 1/4 inch per foot. Where impractical and approved by the AHJ, 4 through 6 inch sewers may run at 1/8 inch per foot. 120 x 1/8 = 15 inches.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 718.1
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A welded steel gas line is pressure tested at 60 psi. Under CPC Section 1213.3, what is the minimum time the test must be held?
CPC Section 1213.3: for welded piping, the test pressure shall be not less than 60 psi and shall be continued for a time satisfactory to the Authority Having Jurisdiction, but in no case for less than 30 minutes.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1213.3
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Under CPC 609.4, when must the hot and cold water supply system be tested?
CPC 609.4 requires the hot and cold water supply system to be tested with water or air upon completion of a section or of the entire system, at a potable water test pressure greater than or equal to the working pressure.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 609.4
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Under Government Code 4216.2, when must an excavator notify the regional notification center (811) before digging for a building sewer?
Government Code 4216.2 requires the excavator, except in an emergency, to delineate the area to be excavated and then notify the appropriate regional notification center at least two working days, and not more than 14 calendar days, before beginning the excavation.
Source: Government Code 4216 to 4216.24 (Underground Service Alert: excavation and 811) GOV 4216.2
37 / 60
Under CPC 707.4, how many cleanouts does a long run of piping in a horizontal drainage line need along its length?
CPC 707.4 requires each run of piping more than 100 feet in total developed length to have a cleanout for each 100 feet, or fraction thereof. Each horizontal drainage pipe also needs a cleanout at its upper terminal, plus one for each aggregate horizontal change in direction exceeding 135 degrees.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 707.4
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Under CPC Section 906.4, how far above the surrounding ground must a vent pipe for an outdoor installation extend?
CPC Section 906.4: vent pipes for outdoor installations shall extend not less than 10 feet above the surrounding ground and shall be securely supported.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 906.4
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Under CPC 706.2, which fitting may a horizontal drainage line use to enter a vertical stack?
CPC 706.2 lets horizontal drainage lines enter a vertical stack through 45 or 60 degree wye branches, combination wye and one-eighth bend branches, sanitary tee or sanitary tapped tee branches, or other approved fittings of equivalent sweep. Double sanitary tees are allowed only where the barrel is not less than two pipe sizes larger than the largest inlet.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 706.2
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How long must a DWV water test be held to determine if the system passes?
CPC 712.2: the water is kept in the system for not less than 15 minutes, and the system must be tight at all points.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 712.2
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Under CPC Table 313.3, how must a vertical cast-iron hubless soil stack with shielded couplings be supported?
CPC Table 313.3: vertical cast-iron hubless pipe with shielded couplings is supported at the base and each floor, not to exceed 15 feet.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 313.3
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Under CPC 609.10, when a new or repaired potable water system is disinfected, what is the first step?
CPC 609.10 requires new or repaired potable water systems to be disinfected prior to use where the Authority Having Jurisdiction requires it. The procedure starts by flushing the pipe system with clean, potable water until potable water appears at the points of outlet; the chlorine solution comes after.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 609.10
43 / 60
Under CPC 314.4.1, thermoplastic building sewer piping must be bedded in at least how much granular fill?
CPC 314.4.1 requires thermoplastic piping to be bedded in not less than 4 inches of granular fill supporting the piping, with backfill compacted along the sides in 6 inch layers to not less than 12 inches above the piping.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 314.4.1
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A PRV on a supply system is set to deliver 65 psi downstream. The incoming city pressure is 100 psi. What is the pressure drop across the PRV?
100 psi (incoming) − 65 psi (downstream) = 35 psi pressure drop across the PRV. The valve regulates and absorbs this difference to protect downstream fixtures.
Source: Arithmetic from the question
45 / 60
Under CPC Section 609.4, when a potable water supply system is tested with water, what must the test pressure be?
CPC Section 609.4: the potable water test pressure shall be greater than or equal to the working pressure under which the system is to be used.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 609.4
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A sewer trench will run parallel to a house and be dug deeper than the footing. Under CPC Section 314.1, where must the trench be located?
CPC Section 314.1: trenches deeper than the footing of a building and paralleling it shall be located not less than 45 degrees from the bottom exterior edge of the footing.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 314.1
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Under CPC Table 313.3, what is the maximum horizontal support interval for 1 inch copper water pipe?
CPC 313.3 requires suspended piping to be supported at intervals not exceeding Table 313.3, which lists copper 1 1/2 inches and smaller at 6 feet horizontally and 2 inches and larger at 10 feet.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 313.3
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Which type of backflow prevention device is required at an outdoor hose bib (frost-proof faucet)?
CPC 603.5.7 requires potable water outlets with hose attachments to be protected by a nonremovable hose bibb-type backflow preventer, a nonremovable hose bibb-type vacuum breaker, or an atmospheric vacuum breaker installed not less than 6 inches above the highest point of usage. Where freezing occurs, a listed self-draining frost-proof hose bibb with an integral backflow preventer or vacuum breaker is used.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 603.5.7
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A vent terminal is 6 feet from a part of the roof used for parking. Under CPC Section 906.3, how far above the roof must the vent extend?
CPC Section 906.3: vents within 10 feet of a part of the roof used for assembly purposes or parking shall extend not less than 7 feet above the roof and shall be securely stayed.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 906.3
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Under CPC Section 1210.3.4, gas piping inside a building is prohibited from being installed through which of these?
CPC Section 1210.3.4: gas piping inside any building shall not be installed in or through a clothes chute, chimney or gas vent, dumbwaiter, elevator shaft, or air duct, other than combustion air ducts.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 1210.3.4
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Under CPC Section 905.1, how must a horizontal vent pipe be graded?
CPC Section 905.1: vent and branch vent pipes shall be free from drops or sags, and each vent shall be level or graded and connected to drip back by gravity to the drainage pipe it serves.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 905.1
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A 3 inch vertical drainage piping stack carries 45 fixture units. Under CPC Table 703.2, is that load within the limit?
CPC Table 703.2 allows a maximum of 48 fixture units on 3 inch vertical drainage piping, so 45 is within the limit. The 35 fixture unit figure applies to 3 inch horizontal drainage piping.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 703.2 (cells)
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A building sewer 8 feet long runs in a straight line from a building drain that already has a cleanout. Under CPC Section 719.2, is a cleanout required where the sewer connects to the building drain?
CPC Section 719.2: where a building sewer does not exceed 10 feet in length and is a straight-line projection from a building drain that has a cleanout, no cleanout is required at its point of connection to the building drain.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 719.2
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Under CPC Table 703.2, what is the maximum DFU load for a 4-inch horizontal drainage pipe at 1/4 inch per foot?
Table 703.2: a 4-inch horizontal drainage pipe carries a maximum of 216 fixture units. 256 is the 4-inch vertical value, not the horizontal one.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 703.2 (cells)
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A plumber uses a 90° elbow to transition a horizontal kitchen sink drain (1 1/2") directly to a vertical stack. What is the code issue?
CPC 706.2: a horizontal drain entering a vertical stack must use a 45 or 60 degree wye, a combination wye and eighth bend, a sanitary tee or sanitary tapped tee, or another approved fitting of equivalent sweep. A plain short 90-degree elbow is not one of them.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 706.2
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A bathroom has a 1.6 gpf gravity-tank toilet, a shower and a lavatory. All three drain to one 3-inch horizontal branch. Under Tables 702.1 and 703.2, is that acceptable?
Table 702.1 (private): 1.6 gpf gravity-tank water closet 3, single-head shower 2, lavatory 1, for 6 fixture units. Table 703.2: a 3-inch horizontal drain carries a maximum of 35, so one 3-inch branch can serve all three.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 703.2 (cells)
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A water service and a building sewer made of a material other than those approved for use inside a building will share one trench. Under CPC Section 720.1, where must the water pipe be placed vertically?
CPC Section 720.1: when such sewer piping shares a trench with water pipes, the bottom of the water pipe shall be not less than 12 inches above the top of the sewer or drain line.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 720.1
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A new plastic (ABS) drainage and vent system is ready for its rough test. Under CPC Section 712.1, what test medium must be used?
CPC Section 712.1: drainage and venting systems shall be tested with water or air, except that plastic pipe shall not be tested with air.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) 712.1
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Before calling 811, an excavator must delineate the area to be dug. Under Government Code Sections 4216 and 4216.2, what color is used to delineate the proposed excavation?
Government Code Section 4216.2: before notifying the regional notification center, an excavator shall delineate the area to be excavated. Section 4216 defines delineate as marking in white the location or path of the proposed excavation.
Source: Government Code 4216 to 4216.24 (Underground Service Alert: excavation and 811) GOV 4216
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A branch drain in a house serves a 1.6 gpf gravity-tank water closet, a bathtub, a shower and a lavatory. Using CPC Table 702.1 private values, what is the total DFU load?
Table 702.1, private: water closet 1.6 gpf gravity tank 3.0, bathtub 2.0, single-head shower 2.0, lavatory 1.0. Total 3 + 2 + 2 + 1 = 8 DFU. The 4.0 value for a 1.6 gpf water closet is the public column.
Source: California Plumbing Code (CCR Title 24, Part 5) (2025) Table 702.1