New sink is lower...need to lower drain?

[plumbbob]

Hi - we're putting in a new kitchen sink, and it's about 6 inches deeper than the old one...so now the plumbing needs to come up substantially after the trap. Is that ok? Should I cut the junction in the wall and drop it down to match the new level?

Thanks, Matt

[Deb]

Nope, it is not okay. You cannot go up after the trap. And, the kitchen can be tough to alter, since most kitchen sinks have windows over them, what is coming out of the wall is usually just a horizontal trap arm that runs to one side of the sink or the other and then the drain drops down and the vent goes up. You cannot just cut into the wall where the pipe comes out of the wall and lower that piece. The entire horz trap arm, the san tee, vent, and drain connection would have to be lowered.
Code does allow a 4" trap seal, so if you are close, you may be able to get a trap with a deeper seal, but otherwise, it is really usually quite an ordeal.
Deb
The Pipewench

[plumbbob]

Makes perfect sense to me. We're not under a window so it's pretty easy to cut out the san tee and lower it (the vent piping can stay the same, right?) for the right height.

Thanks again, Matt

[hj]

I assume this is a double sink, and if so, first check whether you could install separate traps for each sink and make the connections without lowering the drain.

[Deb]

If you lower the san tee, you lower the vent--the vent comes out of the top of the san tee.
Here, we cannot put 2 traps on 1 trap arm.
Deb
The Piepwench

[hj]

I have put three on one trap arm using a double "Y".

[srdenny]

If you have a double sink, there a couple types of continuous wastes that can save a few inches. Also, there is something called a low inlet trap, which would work for both a single and a double bowl sink. However, if your trap arm is partially about the bottom of your new bowl, you would be wise to call a plumber and have him open the wall and lower the waste tee.

[hj]

A low inlet trap should only be used in the most extreme situation and when all else fails. The inlet socket is only about 3/8" deep so the slip washer has to be very tight and the tailpiece cannot be even a little bit short, or the least "bumping" can cause it to come apart.

[srdenny]

[COLOR=Navy]A low inlet trap should only be used in the most extreme situation and when all else fails. [COLOR=Red]I would say wall surgery qualifies for an extreme situation. 17 gauge low inlet traps with afat o-ring for the inlet washer generally handles any bumps and grinds which might occur under the average sink.

[hj]

A low inlet trap only enables a "close" connection to be made. Lowering the pipe in the wall would be an "extreme" situation, but should only be used when all else fails. The water lever in the piping to the LI trap will be about 1 1/2" above the end of any tailpiece going into it, which could cause a continuous waste arm, for example, to be "under water" which would affect its drainage, and if there is a garbage disposer could make the situation unacceptable.

[srdenny]

If the continuous waste and or the disposal outlet are below the top of the waste arm, it's surgery time. In cases where they're a little higher, a low inlet trap will work. Often in a two compartment set up with the waste stubbed out 14" or more AFF, a disposal waste is to be preferred to a continuous waste. Coming strait off the disposal outlet and into the baffle tee it saves about 2" of fall, thus allowing a longer tailpiece on the baffle tee and ensuring that the trap connection and thus the arm of the low inlet trap is below the horizontal run of the disposal discharge. If this can't be achieved, as hj says, underwater conditions will ensue.