The drain connection at the wall is too high on this sink, resulting in a 9-inch-deep trap seal — 5 inches deeper than is allowed by code.
The drain connection at the wall is too high on this sink, resulting in a 9-inch-deep trap seal — 5 inches deeper than is allowed by code.

A.Mike Casey, a licensed plumbing contractor and co-author of Code Check Plumbing, responds: When a trap is too shallow, the trap seal — the slug of water that remains in the trap and blocks sewer gas from entering the house — is more likely to evaporate. When the trap is too deep, liquid may flow through it too fast, which can lead to siphoning of the trap seal and sludge buildup.

To prevent these problems, plumbing codes require that the water seal in a trap be between 2 and 4 inches deep (2006 IRC, P3201.2). If installing a sink with a deeper bowl results in a trap seal deeper than 4 inches, you’ll have to open up the wall and relocate the trap arm connection at the drain (see photo, above). Remember, too, that the trap...

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