Used plastic water tank with 110 ac - 1650 watt electric heating element. It has a flat bottom 18" with fill at the top and a single outlet at one end 12" high 64" long. This was in the rafters of a hunting camp and used for gravity fed shower. This factory designed tank produces hot water with a normal on / off switch, I recommend a lighted one. It will produce boiling hot water if left on unattended.