I have a holding tank on rv, non potable water that I need to heat up to drain . I live in northern Alberta, so the average temperatures are -20. I don't want to wreck anything or gas myself out. I am looking for over the counter chemicals.
I'm assuming you only need to liquefy ice to drain a septic/grey water tank. Calcium chloride (sold as damp rid) will melt ice down to $-56^\circ C$. Just add about 10 Pounds to the tank wait a few hours (perhaps even drive a little to slosh it) and drain.