We used to have one kind of like that...ours was made out of a piece of old tractor innertube that had been sealed shut on the ends. We laid it up on top of the camper. You would pump water into it with a pticher pump then shut the valve off. By late afternoon on a good sunny day you would have about 5 gallons of HOT! water. If you were careful you could get a decent shower out of it

'Course on a really hot day you could go jump in the pond to cool off, so who needed the shower
Wonder if the one you have there works as a thermo siphon system?
Aaron
