Tank - outlet hose goes to pump inlet - pump outlet to di vessel inlet - di vessel outlet to hose reel - hose reel to pole and brush.
Might be worth getting a couple of water butts or an IBC and having them filled all times back at home.
Drop in a submersible pump and whenever you need to fill the tank in your van, just take off the van tank lid, put in large diameter hose from submersible pump, plug pump in and your van will be full in about 2 minutes.