If I have back-to-back meetings, I'll leave a few minutes early (with apologies) and also apologise to the next meeting if I'm late. If anyone calls me out, I'll apologetically claim "biological imperative". If they don't understand, I tell them that my bowels wait for no one. That is enough to get everyone to move on. No one wants to talk about someone else's bowels.

“Time for a bio break.” I’ve heard that often.

Sometimes, when I need to pee, I say "I need to pee". I find this complex, advanced strategy works pretty well.