Need Help With 1999 Northland Polar 860 Extended Cab

I don't know about the Northland but my experience with truck campers is that there isn't a low point drain. The lines are so short you either fill them with antifreeze or blow them out by opening the faucets, etc. There is a drain on the hot water heater and you just pull the plug and anode rod to drain it. I suspect yours is similar.