garbage disposal causing minor backup in double sink

[homey6660]

I installed a garbage disposal and new pvc pipes under the double-sink in my kitchen. I've had sporadic and very minor bouts with water coming up through the adjoining basin when I run the garbage disposal (the water barely gets from the drain into the actual basin). Any ideas why this is happening? Is it normal? I have attached a picture of my setup if that helps.

Thanks in advance for your help.

[Clayton]

The rough-in for your kitchen sink drain is too high for the installation of that garbage disposal. Your fixture drain (trap arm) is coming out of the wall so high that you had to install the J-bend of the p-trap backwards to get it connected. The backwards J-bend gives you a very deep trap seal which is not going to let the garbage disposal drain very well. Food particles will probably start collecting in the trap because of the deep trap seal. If the drain turns verticle there where it goes into the wall it might not be to hard of a job to correct this. By cutting open the wall and removing a section of the verticle drain and install a tee for your drain a few inches lower. This should allow for the proper p-trap and drain installation of your garbage disposal.

[RioHyde]

In addition to what Clayton said, if the tee between the garbage disposal and the basket strainer isnt a center outlet baffeled tee you'll get water traveling from the disposal side to the other bowl.

[hj]

For one thing the tee is not a baffle tee, so the disposer shoots water right across and up into the other sink's drain.

[homey6660]

I've had a couple of conversations off the public board that were helpful and I figured I'd take them here now. I've copied them below. Wonder your thoughts on Clayton's suggestions and whether or not there are other alternatives, too. Also, the center tee is baffled. Thanks to all who have responded thus far. Here's the text (most recent to oldest):

Quote:
Originally Posted by homey6660
Here's a newbie follow-up question for you...is there a way to sorta shrink the j-bend connection. Meaning, if I had that center tee shorter, it wouldn't be such a deep trap and the water would flow easy enough through that shorter length. I know that probably isn't very clear. I guess it might be easy to think of it as a short "U" instead of a "J". Does that make sense? If you understand what I'm asking, is what I'm asking possible? I'd just rather avoid cutting into that waste pipe because I'm perfectly fine working with the kits or the (can't remember the name, but the parts that basically screw together).



Yes there is a p-trap like you are asking about. It is called a "low inlet trap". Designed just for your situation except I think it is just a 50/50 chance that it will solve your problem. It will remove the deep trap seal so that is great, but without much verticle drop from the tee to the top of where the water level in the trap will be setting the waste water may still try to back up a little. I would bet the water will still travel across the tee and may start to come up the verticle part of the drain, but hopefully it wont back up all the way into the sink compartment.
Anyway, it is sure worth a try so you don't have to cut open your wall.

All the low inlet traps I've seen are chrome. I know they make them in plastic but I've never seen one available anywhere. http://img.photobucket.com/albums/v...ng/lowinlet.gif

If all else fails... buy the correct size (i would think 1-1/2") sch. 40 pvc wye, two trap adapters and some pvc glue and primer. Cut the drain off coming out of the wall. Install the wye onto that drain pipe and the two trap adapters on to the wye. Use the low inlet trap on the garbage disposal with the factory supply drain elbow and install the standard p-trap on the other sink compartment. Make sure the use of the factory drain elbow and low inlet trap will allow you to be high enough to connect with the drain in the wall before trying that.

Good luck
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Quote:
Originally Posted by homey6660
What is the rough in? At first, I thought it was the line going through the wall, but you then call that the trap arm.



Yes, the line going into the wall.

more info... "rough-in" in this case means the measurement from the floor to the drain coming out of the wall. Trap arm is the horizontal section of drain from the j-bend until the drain connects to a vent. A tubular p-trap is made up of thin wall tubing consisting of the j-bend and waste arm.


Quote:
Originally Posted by homey6660
Which part is the very deep trap seal?



The j-bend.... notice how much less water the j-bend would hold if you turn it around the other way. The garbade disposal "pumps" the waste and water out and this extra depth of water being held in the j-bend adds resistance to the pumping force and allows the water to back up into the other sink.



Quote:
Originally Posted by homey6660
If I understand correctly, are you telling me to cut the hole in the wall to get at the line there and cut out a piece closer lower than where it comes out and then put in its place a tee (with the two holes line up going vertically and the one coming out to the drain arm)? That tee would then connect to the trap at a lower point?



Yes, but you need to make sure the drain does turn verticle there. Sometimes the drain is installed traveling horizontally accross the wall several feet before turning down (because of a window above the sink). If your drain continues horizontally beyond this cabinet compartment, it may be very difficult to add a tee and run a new drain horizontally at a lower level.
To know where to rough-in (how high to stub out) the lower drain, remove the j-bend and waste arm, and reinstall it onto the tee the correct way. Rough-in the new lower drain at this point or near it, as you have room to cut off more of the tee if the rough-in is a little high (it is always best to be a little low as you are finding out now).


Quote:
Originally Posted by homey6660
One thing is that I copied exactly the pipe layout that existed before I installed the disposal and new plumbing/pipe. I changed out all the pipe because it was very old. I never had problems with that previous set up (it had the backward J). Why didn't I have the backup issue with the previous set up?



Did the previous set up have a garbage disposal or just to standard sink drains? As I mentioned earlier, the garbage disposal does force the water and waste out and this allows it to push it up into the other sink compartment because of the added restriction of the deep trap seal. However, if your drain is partially clogged or a little sluggish this could cause the same problems, but I would bet it is the deep trap seal.