I just made one this spring and it works great. It's a slightly different design than the ones you normally see explained. Been meaning to start a thread on it so others can build one as well. It cost me less than $50. I'll start working on putting the instructions together for you later when I get to the computer.
? They run as long as pump pumps THEN you better pull that hose outta your wetsuit as less flow means more heat and you will weld your arse shut. Same same starting up as takes a few minutes to warm up,always use a holding tank so you'll never burn yourself as they give you more than ample time to notice heat increases. With new closed cell tech on wetsuits I haven't had to use one since 2006. Gotta wear more weights but ok as still snug as a bug even in the SF American-John