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LeviDIY 04-12-2010 09:48 AM

Lowering kitchen drain pipe - PVC
Hi all - I'm at a cross roads in terms of DIY vs. call a plumber. Here's the sitch..

Remodling kitchen DIY mostly. Ripped out to studs, rebuilt wall, cabinets in and had the granite guys put on the counters w/ a sink. Old sink was top mount, new sink is undermount...

You guessed it... I didn't think ahead to lower the drain pip an inch or so and now, with disposal, everything is off by about an inch. My initial stop gap measure was to reverse the P trap to lower by the extra inch (I thought this was genious :jester:), but now every time we run the disposal, that connection gets shaken and leaks (bucket underneath temporarily). I've looked around and the smart solution here seems to be opening up the wall (cutting out some of the back of the cabinet) and lowering the drain pipe in the wall.

My question is: before I cut open the back of the cabinet and my nice fresh drywall behind it, should I do that or call in... I guess, what's involved in this process, step by step or anyone have a diagram/link to post? :thumbsup:

My "plumbing" resume is this: switched out toilet, installed new shower heads and faucet valves in bathroom reno, installed new sink faucet in bathrooms and kitchen, but no change in rough in plumbing.

Any advice, encouragement, or discouragement? :) Let me know if you need more info on materials, pictures, etc. Thanks!

plumbdoc 04-12-2010 11:13 AM

use an 1 1/2 abs glue type trap
Use a 1 1/2 abs or pvc glue type trap. when you use one of these traps you can add a pvc 1 1/2 union to the short bend 90 and add a piece of pipe to the trap to lower it. No it does not pass code but it will work without tearing the wall or cabinet out. picture the pipe coming out the wall with the trap 90 facing down. glue a pvc union on the trap 90 so the pipe is going towards the ground. now glue on your trap. you have just lowered the trap by a few inches. its kind of hard to explain they dont make a fix for it on the shelves. so you have to think and make one that will work. this will fix your problem and not leak as long as you do it just like i said. Hope this helps.

LeviDIY 04-12-2010 12:11 PM

plumbdoc - thanks for the reply.. I'm concerned about drainage within the disposal, and have thought about jury-rigging something like you've written up, but really am looking for advice on the feasibility of lowering the drain pipe, given limited DIY-manship.

plumbdoc 04-13-2010 11:08 AM

It sounds to me like the feasibility is a pain in the A**. didnt you say you would have to cut hole in the back of the cabinet and then sheetrock to get to drain pipe. What i suggested would work fine. No leak and should drain fine from disposal. But if you want to lower drain pipe that would be the best bet! I just hope the plumber didnt put in a dirty arm (ran the drain horizontal in the wall before stubbing out) or you might be wasting your time cutting into the wall.

Also you might want to call a plumber and have him take a look and see if he can rearrange the plumbing under the sink to make it work. Is there two drains in the sink or just the one for the disposal?

LeviDIY 04-13-2010 11:31 AM

thanks again... working with single sink set up here.. I may "temporarily" (read: not looking forward to a plumber's bill anytime soon) try PVC glue... but never used it, only those nuts on the Home Depot-sold pieces... any advice for a PVC gluer first timer?

rjniles 04-13-2010 12:51 PM

Cut out the back of the cabinet, a piece about 6" wide and 12 " tall should do it. Open up the drywall and lower the trap arm. Use a Fernco connector for the upper end of the vent line. Don't worry about the hole in the drywall as no one will ever see it. Cut a patch of Luan plywood about an inch bigger in each direction that the hole. Cut a hole in the Luan for the trap arm and screw in place over the hole you cut. Stain to match cabinet if you are fussy.

LeviDIY 04-13-2010 12:56 PM

see its the actual lowering of the trap arm and vent line... I am wondering how that is specifically done.

rjniles 04-13-2010 01:32 PM


Originally Posted by LeviDIY (Post 428202)
see its the actual lowering of the trap arm and vent line... I am wondering how that is specifically done.

In the wall you will find a tee, drain going down, vent going up, trap arm coming out of wall. Use a sawzall (or what you have) to cut the tee off top and bottom. Cement a new tee on the drain (pipe going down) (this will lower the trap arm about1.5"- If you need more cut some more off the drain pipe), cement a short piece of PVC going up and connect with Fernco connector. Bring a stub oit of wall for new trap arm. Install you cabinet patch. Holding the P trap in place determine where to cut off the trap arm stub. Install a trap adapter on the trap arm and connect the P trap.

Once the wall is open it will take as long to did it as it did for me to type this. I am a slow typist:)

BTW, a previous poster mentioned a dirty arm. This is a pipe that goes right or left after it goes into the wall. The reference means that it is both a drain and a vent It is also called a wet vent. . This is sometimes done to avoid a window directly above the sink. If you find this check back with the group on how to proceed. It is more work but it is doable.

plumber Jim 04-14-2010 04:05 PM

Before you cut that wall open post a picture of the underside of your sink. the tee may not be in the wall right behind your sink unless you remember seeing it right there before you drywalled. Some go horizontal then run to the tee on the left or right. Post a picture and we can see if you have any other options.

Alan 04-14-2010 09:19 PM


Originally Posted by plumber Jim (Post 428723)
Before you cut that wall open post a picture of the underside of your sink. the tee may not be in the wall right behind your sink unless you remember seeing it right there before you drywalled. Some go horizontal then run to the tee on the left or right. Post a picture and we can see if you have any other options.

x2 on this.

I wouldn't hesitate if it was just drywall, but since there' s a cabinet back involved i'd post a picture.

oh'mike 04-15-2010 06:50 AM

Levi---This happens all to often!

The advice you have been given is right on the money--Open the cabinet and drywall--

You will see what parts you will need as soon as it's open.

Once the new tee is installed--and the cabinet back is patched--

Loosely install the two P-traps and figure out the neatest arrangement of T's or Y's or whatever will give you the most room under the cabinet.

If you had a single P-trap set up before now is the time to do it right,One P-trap per drain is code here----May not be where you are --but it will give you a more trouble free drain system.


LeviDIY 04-15-2010 08:35 AM

I'll get ya'll a picture tonight when home from work... thanks!!

LeviDIY 04-18-2010 09:41 AM

2 Attachment(s)
Here are a couple pictures... not the greatest detail, but let me know if you need more, or a different view/angle. The black elbow is coming out of the disposal and remember, the P trap right now is reversed going into that and then the drain coming horizontal from the wall..
Attachment 19700
Attachment 19701

It appears that the exit from the disposal is now essentially even with the drain pipe heading into the wall... ideally that should have a downward slope to it, correct? Would this lead to slow drainage?

oh'mike 04-18-2010 05:32 PM

Levi--Good enough pictures--Is that a single sink set up?

Before you start cutting---loosely install the p-trap correctly so you know the minimum distance that the T must be lowered.

The pipe may be 2" going down--and 1 1/2 going up to the vent.

T's are available with 2--1 1/2--1 1/2 openings --That's why I suggested you open it up first--
then go shopping.

The garbage disposer can easily be loosened and turned or removed---There is a silver collar where the machine meets the sink---it has three rings on it --just the size to stick a heavy phillips screw drive into.

Slip a screw driver into a ring and give it a pull--1/4 turn and the machine is loose.

---Mike--Good luck--Have fun--

Alan 04-18-2010 07:17 PM

We rough in kitchen sink drains at 16" from the floor. This should give you plenty of room, although double check first in case for some odd reason you have a super low countertop and extra deep sink. :eek:

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