Sewage smell when washer drains

[Andrew4343]

We have had a sewage smell that was getting worse by the day. We have reseated a toilet that was clearly a problem, which temporarily fixed that issue. We have replaced a potentially faulty AAV valve which semi fixed the issue. We have done a smoke test and it showed no leaks...
Now the smell seems to only come back when the washer drains. I have made sure the drain pipe isn't going past the trap. We think that maybe a trap is not vented properly and the large amount of water being drained is siphoning a trap dry.
The smell never seems to come from the same place, and it never smells around the laundry room. Why would the smoke test not catch the problem? Does anyone have any ideas?

 

[EmyJ]

Remember that all drains to a sewer system have a "P" shaped trap filled with water. The trap provides a seal to keep out sewer gas.The seal is eliminated, allowing sewer gas (and smell) into your house.
The solution is quite simple easy pour water into the drain.
Every fixture usually has traps and vent pipes to keep smell from entering.
If missing you may need a plumber to install them immediately.