I think they moght be right about him being a plumber and stealing parts. I can't think of any other reason for it other than he could have had a bet with his mate or could just simply be a madman. :-P
Which pub or club or hotel in the area has had a nice 'new' piece of porcelain installed of late? Find that and asked who installed it and you will have the 'pisser taker' 'bang to rights' as they say.