I transfer water via a 1 .5 h.p swimming pool pump from 3 ibc tanks link together all pipe work must be 2" imperial on the suction & discharge end use a 2 " gate valve to stop water drainage but dont use the valve to turn water off when your filling van install socket with switch for pool pump in garage in sight of your van tank, keep a eye on level of tank use 2" x 4 metre Flexible hose to van tank or what length you require when the water approaches the top simply turn off at switch and turn gate valve off job done.
Note water will fill a 650 litre tank in 4 minutes so no tea break you can buy this pump from Machine mart 2 "imperial swimming pool pipes and fittings must be solvent weld these can be purchased from Preston plastics or maybe Ebay.