Bibulous (etymologically related to imbibe) can refer, then, both to the sponge and to the person who drinks like a sponge.
From James Joyce's Ulysses:
"The hoi polloi of jarvies or stevedores or whatever they were after a cursory examination turned their eyes apparently dissatisfied, away though one redbearded bibulous individual portion of whose hair was greyish, a sailor probably, still stared for some appreciable time before transferring his rapt attention to the floor."
And no, you shouldn't infer anything from my posting this word, with a quotation from an Irish author, on St. Patrick's Day. It's just a happy coincidence, certainly.