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Q.My client’s kitchen sink has a shallow 6-inch-deep bowl, and the drain connection is located in the wall rather than the floor. She would like to replace the sink with one that has a much deeper bowl, but that will place the bottom of the bowl at nearly the same level as the drain opening. Is it okay to use a deeper trap and the same drain opening, or will the drain opening need to be moved to accommodate the deeper sink?

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.

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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.

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 arm on the discharge side of a trap must be at least two pipe diameters long and should slope 1/4 inch per foot toward the vertical discharge (2006 IRC, P3105.3).