Hamguy was spot on, I'll summarize for clarity:
The A-Frame Hot Water Heaters have electronic ignition with no standing pilot light. The heater ignite using an electronic spark when flame is needed to heat the tank water. This is controlled exclusively on the A-Frame models with a switch inside the camper. On and it will ignite as needed, unless there's a fault (no ignition) in which case a light comes on indicating it didn't light. I believe in a fault condition you have to cycle it off and back on to try again.
As Ham said, make sure the heater is full before turning on the switch by using the pressure relief valve at the top of the heater on the exterior of the heater (behind the cover on the driver side front of the camper). Running the heater without a full tank will cause damage to the heater.
Ham's explanation on the drain also is perfect. I've not added an elbow and extension, and just use garden hose and put up with the slightly slow draining and gurgling
As others have said, hook up to city water before you head out and fill your hot water heater tank and all the lines by running both hot and cold at the faucet (and or outside shower) and be sure again to use the pressure relief valve to ensure a full hot water tank.
Most of us travel with an empty fresh water storage tank to save the extra weight and will fill at the camp ground if no city hookup available, then drain before leaving.
Bonus Tip: When leaving the CG, open the fresh water drain valve and leave it open on the drive home. This will empty the tank near 100% as the water sloshing around will work it's way over to the drain which is higher than the bottom of the tank.
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