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I recently came across a problem that is fairly common in remodeling kitchens. A client remodeled their home after 35 years and ended up with a nicer, under mount sink. The sink bottom ended up about 4″ lower than the previous one too, so the connections to the wall needed to adjusted to make it all work.
This usually comes as a surprise to everyone and if your kitchen cabinets have backs it can be a real problem to fix. If you are gutting the kitchen, always lower the sink drain.
Shit goes down hill
The first rule of plumbing is “Shit goes down hill” this means that in most situations we like to see 1/4″ per food of slope. That being said, if the P trap ends up too low in the cabinet for the drain to work you are not going to get your required slope.
What really needs to happen is that the drain needs to be lowered in the wall but that can be very involved. In the event that you have a garbage disposal dangling beneath the sink it can compound the problem. One client decided not to have a garbage disposal after discovering the problem too late.
On the off chance you can put everything together and the water trap is not being made in the garbage disposal, then you can use one of these unconventional techniques.
The not so common solution
When it came to installing the drain we were about 4″ of. When I swung the P trap around it would have just worked but there is no way to connect the P trap backwards without some special fittings.
Here are three solutions.
- Use a threaded connection and a 1 1/2″ ID coupling to a 1 1/2″ OD with a threaded connection that is designed to accept a tapered ring and installed the gizmo after the backwards P trap. It was able to make up the 2″ gap.
- Another way to do it is to switch to a metal p trap, but you would only get about 1/2″ of purchase on the short end. (That messes with the “able to sleep at night” feature of knowing you did it right)
- Create your own P trap out of ABS pipe or PVC pipe and avoid using the typical P trap kit.
- Do it right, open up the wall and lower the drain.
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