One of the problems I see with the glazing solution is the water can get very hot, hot enough to scald (as you said almost to boiling), unless some sort of controller is put in place to stop flow when that happens. This doesn't seem very safe for the swimmers who are hanging out close the returns.

The other thing is, and you said it yourself you have to be careful of melting what is between the glazing, you would have to use some sort of metal (copper?) piping inside the glazing. That increases the cost of the homebrew solution.

When I was searching for solar, I looked the homebrew black pvc runs (ala Poconos), I decided I didn't have enough room to make that type of solar collector efficient. I went with the pool panels, as mentioned before they are the most efficient for the smaller size that might fit on a roof or some other platform. We who are on postage stamp size lots don't have the space that would make PVC piping work (but I do have broadband ). Also add in the cost the necessary PVC connectors (elbows, T's, etc.), the homebrew costs really start to add up fast. You may find some inexpensive ebay panels give you the most bang for your buck.