OK, I've not had sex using SCUBA, but when younger and dumber my wife and I had sex in a lake and in the ocean. Neither time did she develop an infection or other problem. Seems like a varient of the man stanking upright and the woman facing him with her legs wrapped around his waist would work. Seems like that's what we did. Also, to really safe have a third person there to monitor gauges and spot trouble.
Roger
