A stoat is a creature similar to the weasel but bigger.
A water butt here in Britain is a kind of water tank.
p.s we dont say ‘butt’ here. Bum is the word used here for our rear fleshy feature. Also arse, backside, derriere, rear-end or buttocks...
OK, now the story makes sense. The Stoat is what gay Brits use like a giant Gerbil. That explains how it got in the butt.
Not to be confused with the EWnglish meaning for ‘pecker’ ... the nose.