bum-bum or tinkie-winkie?

When I'm strung out on self-raising flour and getting a nice serving of man-sword I often try to work out which one of my two lower holes is getting filled.

(Often it's both, but that's kind of like a trick question).

Usually I just pass out before I can think of the answer, but the other day I realised that I could use this handy rhyme to be sure:

If I can get two dongs in
They're using my bum as a hole of sin.
If I can get three or more
They're making the most of my front door.

Hope that helps anyone else out there.