Many thanks Andrew,maureen, i too have an oklahoma. the drain pipe is not the overflow pipe. the drain pipe with the tap on it is sited on the same side as the water inlet socket, as for the overflow pipe , this is sited on the other side of the onboard tank( door side ). i aslo thought i would mention that when i took the van out for it's first run, i did'nt have a large aquaroll. luckily for me the site that i was staying on, had hosepipes on reels at the water points. i attached the hosepipe to the drain valve, opened the drian valve tap, and aslo the hosepipe tap and hey presto!, filled the tank up.
We made life simpler by buying a Bailey Burgundy, so we don't have an inside tank !! Our friend's tank however,is in the same place as yours.He was going to have a look today,so hopefully he has now found the overflow pipe.
A bit more explanation in the owners handbook would have been helpful.They certainly don't make life easy for those who are not so agile these days !!!
I have no idea Paul.....and it is the sort of thing that I cannot get enthusiastic about :0)Maureen
Glad to have been of service! Will he now be adding the piece of hose as I have done?