You should see what I’ve seen in France!

I now realize a lot of the bad bathroom smells are because of traps siphoning dry. Tho the general lack of exhaust fans doesn’t help. Anywho, AAVs to the rescue! And mineral oil in their version of a t&p valve if it doesn’t need to drain much to prevent evaporation of the trap water: https://fr.wikipedia.org/wiki/Groupe_de_s%C3%A9curit%C3%A9