Green’s Dictionary of Slang

(Irish) to wash; thus possing wet adj., very wet; posser n., one who gets wet.

1922		Joyce Ulysses 341: When she undid the strap she cried out, holy saint Denis, that he was possing wet.
1970		C. Brown Down All the Days 107: Sean – you blondey bastard – keep out while I poss out the floor!
1995		P. O’Keeffe Down Cobbled Streets, A Liberties Childhood 15: She was a generous and loving person and did not mind at all all the slopping and possing out of baby clothes. [Ibid.] 116: You’ll have my good kitchen floor possin’ wet with your andremartins.
2001		G. Coughlan Everyday Eng. and Sl. 🌐 Posser (n): when you get a wet foot from walking in a puddle of water.