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Could you use a wine cork on a smaller version?
Make an X out of 2x4s. You're going to spiral black PVC irrigation tubing through that X by drilling holes in the wood. It takes effort as the radius gets smaller, but you can get the whole 100 feet in there. Then enclose it in a box made from 5/4 deck boards. A back made from Styrofoam painted black and a front made from corregated roofing completes it. You need to make a bypass in your pool plumbing and allow only some of the water into the heater so it sends enough time in the coil to get warm.
Motor Oil works when using wooden forms. But I doubt it would adhere to the plastic well enough.
Works great to clean Camelback pouch and tubing or polyethylene cycling water bottles!
USB powered? That would be SO slick if it could be done!