I dont worry about a bit of water inside the collector. even our hoses have water
inside and that rubber is flexible enough to expand by that amount. I am more
worried about ice jams, but if it is in full sun the water should thaw so water would
move thru it. it is the larger bore hose going to and from that needs to be drained.
I will weight the whole setup before I first move water thru it, then weigh it after
and see how much of a difference.. how much water is left in the system.

I would never trust any solution in the hose near my pond. and the whole idea is to
heat my pond in winter so I dont have to use the 500 watt heater. Ingrid

On Tue, 14 Oct 2008 12:45:18 EDT, Derek Broughton wrote:
That's not a bad idea, but I rather doubt their _pool_ heaters are designed
as "drain-down" units So I'd worry that when you drain it, it would
still have enough water inside to damage the collector.

For domestic hot-water use, we use a system much like Jan describes - a
glycol solution, continuously pumped through a collecter to a heat
exchanger.