I have a double kitchen sink with the ABS dishwasher adapter tied into the horizontal pipe between the sink drains.
It is after the union trap up with the sink drains.. The problem I believe is when the dishwasher completes its drain cycle the union trap seal is left broken, terrible smell coming up through sink drain. Perhaps too much force or its pushing air at the end of the cycle that breaks the internal water seal in the trap (preventing the gases from getting into the sink)? There are no water leaks in the system...

If you look at this (not my pic, example only, and no I don't have a rubber coupler) the dishwasher adapter is missing but mine is near the right sink drain on the horizontal 1.5" pipe... Direction is correct it shoots to the left...



I'm not sure how to resolve this issue?
Thanks in advance!



Edited 4 times.

try loosening the union nut, dropping the trap enough to clean the mating surfaces, put a touch of grease on the surfaces and threads then tighten.

This issue is the line gases are getting through the union trap after the dishwasher drains. The union trap does not leak any water. When I mentioned the seal is broken I meant the internal water seal in the union trap preventing gases from getting by.

Run a little water with the faucet and then drop the trap and measure the amount of water retained by the trap. Run the DW and do the same. See if the retained water is less, ie trap is losing it's seal.

What exactly does that do for me? How do I stop it from happening?

i was taught about the 7 ways a trap can lose its seal.
easiest if you google "how a plumbing trap can lose its seal"
have a read, look over your situation and come back with any questions..

If the retained water is the same, the DW is not causing the problem.