For the past few weeks, the u-shaped tube, attached to the disposal, under the sink has been leaking. Until I could get it fixed, I placed a bucket beneath it to collect the water. Last night, the bucket was full to the brim and as I was removing it I noticed the leak had gotten bigger. After emptying the bucket in the toilet, I went back to the sink and jiggled the pipe and water started to spray from the joint fitting on the part of the tube leading away from the sink into the wall. I went to check on something else and when I returned the sink was full of dirty water (backflow?). I turned on the disposal and let it suck the water out. Then I noticed that each time I heard my neighbors upstairs run the water and close the valve, water would bubble up in my sink. Again, I used the disposal to suck the water out. I panicked and hurried to HomeDepot and got some liquid drainer and poured 8oz down the drain and waited. After 30 minutes oozy, oily water kept backflowing and sitting. I used the disposal again, and poured the remainer of drainer. After a couple of hours the water subsided and I stopped the drainer with a sink plug. I reasoned the neighbors upstairs had gone to bed and stopped turning on their faucet. My question to anyone out there is whether something is obstructing the pipes between my apartment and the one above? Does the problem lie in the leaking u-shaped tube? Does it just need tightening, or do I need to buy a new one? How much do they cost? Is this something I can do myself? What tools do I need? HELP!!!