Today I was doing an inspection on a house and quickly noticed that all the sinks in the home were plumbed with S traps. This is actually no longer allowed and something that should be corrected. If you have S traps under your sinks and been noticing a stinky smell in your house, that’s probably the reason why.

The reason why S traps are not allowed is because water filling in the downstream vertical portion will create siphoning and loss of the trap seal. The trap seal is what prevents sewer gases from entering the home. You can see an example of a bathroom sink with an S trap in the picture below: