Well, ours is a twin, but we have a canister that unscrews to hold an insert...ours is an Omnifilter whole house filter cartridge T01-DS series C.
Ours came in a 2 pack, and I think we got them at Camping World, but most any oriented store should carry the likes.
Don't forget the rubber washer, as it won't seal properly without it...mike
Michael & Tracy
1989 345 Motorhome
CHARTER MEMBERS: FOUR CORNERS UNIT, AND PROUD OF IT!!!
We live for the moment, 'cause when you get there, it's gone...