A verb? He was fishtanking yesterday.
A noun? He's a fishtank, that one.
An adjective? She was one fishtank person.
An adverb? He entered the room fishtankingly.
I think fishtank as a verb and adjective would be cool. “Im off to do some fishtanking”, or even “he fishtankerously fishtankered the s!%# out of that fishtankerer”