This is what I have for my wetsuit. Quite common in NZ. Basically a tapered neoprene tube in the crotch area of the suit that flattens on the end to seal. Only works on two piece suits though.
The process of using is: Make sure everything is located properly before the dive (can't wear anything under suit, old mate slips into the tube). When you need to go either on the surface or underwater undo beavertail of the suit to expose the tube, press around base of tube to make a good seal and let it flow.
Worked pretty well for me so far. We call it a "scupper"
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