Well, I am of those who have never peed in thei wet suit... yet. I do not think it would be a real problem if I had to.
I usually dive from small boat which have no facilities (zodiac size).
This summer we had one day where we waited more than usual on the boat (usually it is about 2 hours), maybe the water was colder. Several divers needed to pee after they had climbed back on the boat. They just remove their wet suit (partially, as the water is 15C, they wanted to redress afterwards) and jumped in the water again! You could tell the crew you really need a bath just after the dive! (It should be easier to pee in a bath suit... and easier to rince).
I usually dive from small boat which have no facilities (zodiac size).
This summer we had one day where we waited more than usual on the boat (usually it is about 2 hours), maybe the water was colder. Several divers needed to pee after they had climbed back on the boat. They just remove their wet suit (partially, as the water is 15C, they wanted to redress afterwards) and jumped in the water again! You could tell the crew you really need a bath just after the dive! (It should be easier to pee in a bath suit... and easier to rince).