I'm guessing this is something to do with Bridge over Troubled Water? Bridge could be a Profanisaurus term for where you put bumwad (which I think is toilet paper?) and troubled water could be an unpleasant toilet (which I think is a chod bin).
Been a while since I've seen a Viz - I don't live in the UK anymore and thanks to covid restrictions I'm not risking going back anytime soon. Makes me kind of nostalgic!