[instrumentally]

Two weeks ago our garbage disposal broke. Despite not working, the sink drained normally. Then 3 days ago, the sink started to back up (i.e. water would not drain from the sink unless you waited a few hours). Yesterday I decided to replace the garbage disposal. I thought that the water draining problem was related to the garbage disposal. It wasn't, however.

I replaced the garbage disposal, remembering to knock out the dishwasher plug at the top of the garbage disposal. The garbage disposal works fine now (i.e. it spins/runs with no noise). However, we still have the drainage problem.

In disassembling the plumbing pipes while installing the garbage disposal, I replaced all the plastic pipes going from the garbage disposal, through the p-trap, and the pipe going into the wall. They really didn't need to be replaced, but I did so anyway. There were no visible signs of blockage or sclerosis, so I was puzzled why the water in the sink would back up (not drain). I tried snaking the line, but there is a 90 degree bend about 18 inches into the wall which the snake would not make it through.

I will add that when water is backed up in the sink, turning on the garbage disposal causes the 5" of standing water in the sink to drain in less than 10-15 seconds. Yet even after this "purge" of water from the sink, the sink will continue to back up if you turn off the garbage disposal and run the water again. You can repeat this exercise over and over again, and turning the disposal on will immediately cause the standing water to drain... except that there will always remain about an inch or two of standing water in the bottom of the garbage disposal if you look down inside the sink throat.

The last clue to this mystery is that when we turn on the dishwasher, dishwasher water will come up the sinkhole into the sink. But again, turning on the garbage disposal cause the standing water to drain very quickly.

Any clues as to what the problem is?

[hkstroud]

No mystery here, you have a blockage in the drain line.
Turning on the disposal makes it act like a pump, though not a very powerful one. It is creating enough pressure to push the water through the blockage.

Snake the drain line. Rent a power snake if necessary. If you absolutely can't get the snake past a turn, go on the roof and run the snake down the vent pipe.

[ballengerb1]

Agree and the clog is caused by food debris not chewed up by the disposal. BTW is this a single or a double sink?

[Milo Dolezal]

No mystery. Blocked drain. Garbage Disposer is not really "pushing" water through the blockage as it has no power to do so. You have to clean the drain as far as the snake goes. It may be 35'. Do it several times. Make sure you use proper cable tip to do so. Then, run hot water in the sink for 10-15 minutes

Milo