To tap my kidney/ see the man

What does this mean?

Thanks in advance.

Slang for urinate. "Tap" as in a beer tap or spigot.

For guys, also known as 'draining the lizard'

This is another one for Gary to compile a list of similar phrases for the archives if we have not done so already.
I have heard men say that they 'must see a man about a horse,' meaning the same thing.

SR