Basically inside the "outer" canister, I have a "inner canister" that holds the resin
this inner one has a grille at the bottom,
and a lid (with no grille) slides on the top
A thick white plastic washer on top of that inner lid.
An O ring between the outer canister and its screw on lid (but no O ring or seal between the inner canister and its (push on) lid
No foam filters.
I hope that makes sense!
thanks for all the replies so far!