My geothermal heat pump will use well water as its source. Once the water has passed through the heat pump it will get discharged to the outdoors.

My question is how to design a frost and freeze proof drain that can withstand temps into the -10 to -20 range.

I have thought of burning the drain line below frost depth where it could drain into a bed of gravel similar to how a septic works. This might cause the local DNR to get bent out of shape. The discharge is clean and untainted water.

I have been unable to find frost proof drains although there are frost proof faucets.

I have seen freeze proof potable water hoses for RV's but these tend to be pricey.

Can a drain be put together with heat tape, insulation?

Advice is welcome.

It depends upon how much discharge there is. A pump could be used. In this way the pump would not be on until water accumulated in a holding area. The pump would then kick on automatically to drain the holding area and dump the water outside. This way no water would freeze since no standing or moving water would be in the outside area to freeze since the pump is inside..