lmao well, it IS a rubber thingy and there is no other way to describe it lmao. You calling me a butthead? lmao lmao roflmao
It it a spare "washer" that goes on the top or bottom of the tank and the carto fits in the center? IDK because I can't see it. Or is it small like a drip-tip o-ring? Or an o-ring that goes in the hole for the carto....or or or.....

. Put a
, Atty, Catt, Deej - skritches!, Bear, Angel, Elf and {{{Kelli!}}} Good to see everyone out and about! 
(idjits)