What's under the sink?

Can anyone describe this cylindrical fitting under the sink? Is it a cleanout for kitchen gunk? An ancient air admittance valve? It’s lurking in my memory, but I can’t recall a name or a purpose.
By the way, I know the sink isn’t vented and is supplied by PB.


Hi to all,

Jeff it is called a drum or tank trap, they are no longer allowed in construction primarily due to them getting clogged up with “Gunk” This must be a pretty old home as I think they have not been installed since the 1940’s.



looks like a drum trap, not an approved trap anymore…

Thanks Gary. As soon as you said it, it all came back to me.