Yes, SS does have a head on the boat but in the last 2 years or so they've started trying to dissuade you from peeing, whether the suit be yours or theirs. (They also try to keep you from using the mask rinse bucket if you don't use the chemical defoggers - in other words if you use good ol' fashion spit).
I personally love the idea of not feeling the need to pee while "dressed", but after I've been on a boat for 3-4 hours, drinking water and juices to stay hydrated, suiting up to be in time to be the first off the boat when possible, and then immersing my entire body in water... ?!?!? Nature calls !
It used to be an old joke to just dip a sleeping persons finger in a bowl of water - try the whole body.
It's not a fun thing, it's just nature. Don't let it ruin your dive, flush as best you can during the dive trips, rinse good each night, and at the end of the dive trip soak in a tub of Woolite for 24 hours before rinsing and drying thoroughly.