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Question DetailsAsked on 12/12/2014

How fix sink that is noisy because too high above waste line (drop too long to trap)?

Sink manufacturer recommended 6 inch vertical distance from bottom of sink to the waste outlet in the wall. Sink was installed with 14 inches from the bottom of the sink to the waste outlet in the wall. The remodeler did not bother moving the waste outlet in the wall. The excessive drop to the trap is causing turbulence which is causing loud gurgling. Short of tearing up the wall and moving the pipes in the wall, is there a way to correct this problem?

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1 Answer


My first thought is that I think you are misinterpreting the manufacturer recommendation - the sink should freely drain - it should not matter is it is 6 or 60" above the outlet if you system is plumbed right - it wants to be free-draining. The 6" elevation difference is a MINIMUM to provide enough elevation difference to provide a meaningful, cleaning flow rate. More should not matter, unless your piping was installed without a vent, which is bad practice.

So - I would listen carefully (use a paper towel tube held against different places on the piping/sink to localize where sound is coming from), to make sure it is the sink and not the garbage disposal or trap that the sound is coming from. Usually, gurgling or gasping sounds, especially if occurring at the end of the drainout cycle as the whirlpool in the sink reaches the outlet, at a sink are due to a partly blocked trap or due to a blocked vent pipe (which can be because of a partly backing up trap submerging the access to the vent pipe). Or due to no vent at all ever having been put in, particularly in older homes - so if your undersink piping is not connected to a vent pipe, perhaps you need a sink or island vent put in to prevent the water in the trap from being partly sucked out because of the high drop. Do not confuse this vent with the vent for the dishwasher - with the dishwasher flexible tubing coming in and out of it. The drain vent will commonly be 1-1/2" drain pipe coming off the top of the drain plumbing, leading to a vent pipe that eventually leads to the roof (usually combined for entire house in normal size houses).

Also - the trap should be plumbed so it drains near horizontally (only slightly downhill) to the stack drain leading to the sewer pipe, otherwise if there is a significant drop from the trap outlet to the stubout of the sewer pipe is causes a suction on the trap and can suck it partly dry causing gurgling and gasping sounds. If that is the case, then perhaps the trap is installed too high and needs to be lowered to proper height.

So - I would first make sure the trap is clean. Then, if the sound is due to the flow racing down through the sink too fast, you could (not knowing how this sink is plumbed) raise the horizontal run from the sink to the trap, or raise the trap inlet to reduce the hydraulic head from the sink to the first place the water will back up. Of course, if you have a garbage disposal this is not normally feasible, nor a good idea as the flow from the disposal should be downhill to prevent stagnation of water in it.

A plumber should be able to solve this for you - find a company with a good old boy plumber who has been in the business a few decades and he should be able to solve it if you can't.

Answered 5 years ago by LCD

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