Or...

"Piss" is strong and somewhat vulgar.

Men say:

I am going to take a whiz.

I am going to talk to a man about a dog.

I am going to take a leak.

I am going to shake the dew off the lilly.

I am going to the men·s room.

I am going to the little boy·s room.

Women say:

I am going to tinkle.  (very old fashioned)

I am going to the loo.  (loo = bathroom)

I am going to the powder room.

I am going to powder my nose. 

I am going to the women·s room.

I am going to the ladies· room.

The ways are countless.