the simple answer is A
I have a van tank system but am taking all but the tank/pump/battery out of my van this weekend and setting up in my shed. With a couple of water butts, I will have a permanent supply of pure water and with a transfer pump, will be able to fill up my van tank as and when required in about...10minutes...as opposed to having my van off the road for 4 hours while I fill the tank up every night.