What slang do you use in your country for going to the restroom?

In Romania the common ones are:

- “Mă duc să dau calul la apă” - going to give some water to the horse.
- “mă duc să dau un telefon” - going to make a phone call

The funniest I heard to this day are:

- “mă duc să dau mâna cu președintele”- going to shake hands with the president
- “mă duc să plătesc formația” - going to pay the musical band.