Tell us about yourself!
there are several folks demonstrating this technique on the web. youtube etc. google hot tub car radiator...of course you wouldn't want a plastic radiator (never heard of such a thing, how does it conduct heat?)
rather than spending $$ on copper a salvaged car radiator works....while yer at it grab the water pump and the whole thing will run off a car battery. there's also this: http://thehomesteadsurvival.com/build-5-gallon-bucket-sink-diy-project/ home made foot pump can be operated under water