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redroc25 09-08-2009 07:20 PM

garbage disposal /double kitchen sink
I had a single kitchen sink w garbage disposal, I bought and installed a new double sink and hooked up the new sink/disposal, drain lines.

My problem now is that when I use the garbage disposal, it shoots the water up out of the other sinks drain!

Any suggestions here would be greatly appreciated.


Thurman 09-08-2009 07:39 PM

Of course the first question I would ask: Did you use the "same/exact" drain lines that were under the original double sink? Second question: Did you put them back in the same/exact order that they came out? IF I remember :laughing: correctly, some of the drain tubes from the sink that DOES NOT have the disposal unit has a built in diverter so the waste water goes downward to drain. It could have been possible to put this piece in upside down, which would let the waste water be diverted up. Check all of your drain pipe sections again, please. Good Luck, David

plumber Jim 09-09-2009 11:43 PM

You need to make sure you use a baffle tee and make sure its installed correctly.

zzyyzx 11-15-2009 02:38 PM

I'm having the same problem as described above and it has done it pretty much since the house was new (5 years ago). I have a dual sink with a 1/3 HP disposal on one side that plumbs into a diverter that goes straight down from the clean side of the sink to the P trap. When I use the disposal a small amount of dirty water splashes back up the clean side. I have completely replaced the plumbing (all 1 1/2 inch PVC) underneath and even replaced the mini-Studor vent. It still happens. Any other suggestions? I've tried the local home improvement places and they're at a loss also. Thanks in advance!

oh'mike 11-15-2009 02:51 PM

In out area plumbing code dictates that two P-traps must be used on a double sink-

The problem of 'backwash ' is eliminated with this arrangement.

Is cutting out the old drain set up an option for you?

zzyyzx 11-15-2009 03:07 PM

Hmmm... I don't think I've ever seen dual P traps on the same set-up, but I haven't really seen more than a half dozen dual sink plumbings as I am strictly a DIY person. I could probably make the dual P traps work, but it would probably take up the rest of the room under the sink as I have my reverse osmosis system and storage tank underneath the kitchen sink also. In the set-up you describe, at what point do the two lines join together to go down the discharge?

oh'mike 11-15-2009 03:28 PM

P-trap on the sink--
P-trap on the disposer--

Loosely install first thing--THEN figure out whether a Y fitting or a sanitary T makes for the easiest fit-up with your drain location.

Good idea to have a new tail piece extension and tail piece washer on hand.

Yes--there is a lot of space gobbled up under the sink--Oh,well--function first-

One of the plumbers here may be able to post a picture of a typical double sink with disposer set up.


oh'mike 11-15-2009 05:32 PM

If you have a straight pipe coming off of your disposer,you will need to get a replacement for the missing 90 that the P-trap attaches to.--MIKE--

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