i had a leak in my basement from an a/c condensate line that was draining to a waste line with a trap and check valve in between. it was determined that the check valve was not allowing the condensate to pass. the new plumbers removed the check valve and installed a taller riser and there is no more leak. they assured me that a check valve is not necessary but i am concerned that there is now nothing preventing sewage or gas from entering the basement if there is a downstream blockage or the tank is full. thoughts? thanks!

In the winter when the AC isn't running and thus producing no condensation for a long period of time, the trap can dry up from evaporation and let gas through.

thanks sum. so can i just add some water to the trap from above? seems like this would be an issue with or without a check valve. do you think a check valve is needed or not?

no other traps have check valves in your house ? why would this one ?

It would be a rare condensate line installation that would even "open" a check valve, especially after the gate starts to get tight.

I agree, check valve not needed on condensate line, just something to cause a problem. In the months when your air conditioner isn't being used you can add some water to the trap once a month and it will be fine.



Edited 2 times.

Actually, a properly installed condensate drain has a "built in trap", and that is what needs to be refreshed periodically.

Here's one way to do it: