for what it's worth....
my outdoor shower is located on a level below my water heater.
To drain, I open the hot water side on that shower, then crack open the TPRV to vent.
Since the hot discharge pipe is located at the same level as the drain plug, it's more or less getting the same result in my thinking.
No I don't drain it every time.
About the need to drain.....I did come back to my campsite once to find TH TPRV dripping. Well I learned form that the the water heater needs an air space. Over time with use, that air space gets filled with water, so once in a while you need to burp the heater (drain it a bit) to let some air in otherwise the expansion form heating will cause it to drip
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