I too tube in a long john 3mm. I've peed in it plenty and found a that if you elevate your feet and legs as close to the surface as possible and sink your butt down the hot fluid will actually "float" upward toward your ankles because its less dense. Then you can squeeze it out with your hands, like toothpaste. That sounds so friggin' disgusting huh? Peeing or not, anything below 60 degrees for extended duration is pretty chilly for me. But a 7mm oughta be pretty comfortable.