I would like to find out what the best way to heat, and bend HDPE pipes? Would it be heating with water, air, or what would be the recommended way of doing it? Any assistance would be highly appreciated.
Not nearly enough information to answer this. Sizes, tolerances, quantities, etc. Keep in mind that elevated temperature forming of HDPE can cause tube collapse, so you may want to fill the tube to prevent this. Perhaps the fill material can be a heat source.