What do you do with your used condom full of sperm?

When you're at a plates house and don't trust her not to dig that shit out of the trash and try to get herself pregnant, what do you do?

Is it as simple as using spermicidal lube?

I'm always the one to take off my own rubbers and tie the end in a knot.

Current tactic is to put the used rubber straight into a baggy in my 'overnight bag' and if I get questioned, just say 'I'm cleaning up'. If questioned about not throwing it in the bin, I'd say 'too late' and redirect conversation.