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What is the minimum trap seal depth under a sink drain?
Sunday, June 19, 2022
The minimum trap seal depth is 2-inches according to the International Residential Code (IRC P3201.2). A trap seal is the standing water in the U-shaped pipe under a sink that keeps sewer gas from traveling backwards through the drain piping and up through the sink into a home. It is measured as shown in the diagram below. Two problems are created when the trap seal is less than 2-inches: the trap water is more likely to be siphoned away during normal usage by the suction created downstream in the pipe, and the trap seal is more susceptible to loss by evaporation.
The maximum trap seal depth is 4-inches, and traps that are not installed by a professional plumber are more likely to have too much trap seal rather than not enough. Excessive trap depth slows drainage and is more easily clogged.
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Here’s links to more articles about PLUMBING TRAPS:
Trap seal diagram - CodeCheck
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