Welcome to GN's Roy, Sorry I cannot advise exact location of drain plug, although they are usually on side of bottom of tank - again usually on off-side.
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Possum; AKA:- Ali El-Aziz Mohamed Gundawiathan
Sent from my imperial66 typewriter using carrier pigeon, message sticks and smoke signals.
I own an Avan caravan. The water tank has a short plastic hose together with a plastic tap. As Dougwe said, facing the road. It drains the tank, almost. Turn it on & when the water stops running leave it on & go for a drive around the block which will empty the tank completely.