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Trade Exam · Module 4

Sink and Lavatory Installation: Supplies, Traps and Flow Limits

Lesson 7 of 9~20 minFree previewCurrent as of September 2026Leer en español

Lavatories and sinks under the 2025 California Plumbing Code: wall-hung fixtures on metal supports, a watertight joint at the wall, hot on the left, a control valve ahead of each supply, faucet flow limits (1.2 gpm residential lavatory, 0.5 gpm public lavatory, 1.8 gpm kitchen faucet), the 120 F limit at public lavatories, waste outlets of 1-1/4 and 1-1/2 inches, one trap with a 24 inch maximum tailpiece and a 2 to 4 inch seal, and the right way to connect a disposer and a dishwasher.

Key Takeaways

  • CPC 417.5: with two handles, the left-hand control is hot, and hot water is connected to the left side of the fitting.
  • CPC 407.2: residential lavatory faucets 1.2 gpm maximum at 60 psi and 0.8 gpm minimum at 20 psi; public lavatory faucets 0.5 gpm at 60 psi; metering faucets 0.2 gallons per cycle.
  • CPC 420.2: sink faucets 2.2 gpm at 60 psi; kitchen faucets 1.8 gpm, allowed to rise temporarily to 2.2 gpm but defaulting back to 1.8.
  • CPC 407.3: hot water from public-use lavatories is limited to 120 F by an ASSE 1070 device or an ASSE 1084 water heater.
  • CPC 407.5 and 420.4: lavatory waste outlet and tailpiece at least 1-1/4 inches; kitchen and laundry sinks at least 1-1/2 inches; service sinks at least 2 inches.
  • CPC 1001.2: one trap per fixture, tailpiece 24 inches maximum, and up to three adjacent sinks or lavatories on one trap if their outlets are within 30 inches.
  • CPC 419.2 and 414.3: a disposer connects through a wye or other directional fitting, no dishwasher drain goes on the disposer's discharge side, and a domestic dishwasher discharges through an approved air gap fitting.
  • Table 603.3.1: a faucet outlet with an effective opening up to 1/2 inch needs a 1 inch air gap above the flood-level rim, or 1-1/2 inches near a sidewall.

Why This Matters

Lavatories and sinks are the fixtures you set most often. The code rules for them are spread across Chapters 4, 6, 8 and 10 of the California Plumbing Code (CPC). This lesson pulls them together: how the fixture is supported and sealed, how the water gets to it, how much can flow, and how the waste leaves it.

Supporting and Sealing the Fixture

  • Wall-hung lavatories and sinks are rigidly supported by metal supporting members so no strain goes to the connections (402.4). Floor-affixed carriers for off-the-floor fixtures for public use comply with ASME A112.6.1M.
  • The joint where a fixture meets the wall or floor is made watertight (402.2).
  • Concealed slip joints need an access panel or utility space at least 12 inches in its least dimension (402.10).
  • Everything else about mounting, from drop-in clips and undermount adhesive to pedestal anchors, comes from the manufacturer's installation instructions, which CPC 402.8 makes mandatory.

Standards: lavatories comply with the standards listed in 407.1, and sinks with those in 420.1. Every 20 inches of rim space on a group wash fixture counts as one lavatory for fixture counts (407.1).

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