Filling up my tank with van locked?

[♠Winp®oClean♠]

You just need a mini Torbeck valve for your tank same as used in toilet cisterns. Must be "side entry" & just fit a male hozelock on the outside of it to fill tank. Jobs a good'un.

Here's the one I have in my tank, so simple to fit & cost peanuts. This one is over 10 years old & has never failed!!

http://www.toolstation.com/shop/p42876