Thanks guys, just bought the 3/4 inch pipe to suit a 12v pump which i have, however going to end up having to buy a larger battery if I keep on with that idea. The spare backpack battery is not, i think providing enough power to the pump as its very slow.
I might just swallow and upgrade to 1'' pipe. I think an electric sub pump would be a better idea, and the neighbours got one going spare!
Planning on transferring pure water from storage tank direct to a tank in my vehicle.
So avoiding filling and carrying barrels.