You can drain it at either location, if you're not going to use it for an extended period of time. If you use the low point drains, you can open the pressure relief valve on the water heater to help it drain faster. If you plan on using the camper in 2 or 3 weeks, there's no reason to drain it out, unless it was hooked up to lousy water.
2012 Jay Flight 19RD
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2010 Tundra TRD DBL Cab (Traded)
1 Spoiled Dog