My double kitchen sink drains into a 2” white plastic DWV pipe that traverses approximately 4-5’ of distance without any slope at all. I used a level to confirm my visual observation: there is indeed no slope to the pipe.
Here’s where it starts:
And here’s where it traverses the next cabinet:
The horizontal pipe seen in both photos has no slope at all. My question: does this look wrong / problematic / against code?
For context, here’s how this pipe attracted attention to itself. My sink backed up Friday night. I removed the P-trap and drained everything. Put it back together, sent some Green Gobbler and went to sleep.
Woke up Saturday morning, ran hot water and saw it back up.
Took apart the P-trap and drained everything again. Used a rubber coupling to attach my shop vac just downstream of where the trap used to be. Nothing came out, and the vac sucked air from the vent stack. Put it all together, plugged the disposal opening, ran water until it backed up and vacuumed through the sink drain. Vac took out all of the water and then sucked air through the vent stack again.
Snaked it with my 24’ x 1/4” auger. Put P-trap back in, ran the faucet for an hour: nothing backed up. Ran the dishwasher: it backed up into the sink. Drained & snaked again. Sent more Green Gobbler overnight.
Woke up Sunday morning, flushed with hot water and did not observe a back up. Currently contemplating whether to run the dishwasher.
Best Answer
A drain pipe should have a 2% slope. This prevents water from standing in the pipes. If there is not enough flow through the pipe, you also have the risk of sediments building up in the tube and clogging it. I would guess that having no slope in the pipe can cause a problem with the dishwasher. I would recommend changing the slope of the tube.