the water will just run straight out the van doors...so get a tank installed as well
You will need a pump to get the water out of the tank and this pump will need to be wired up to a separate, deep cycle leisure battery and have a on/off switch fitted into its wiring.
A relay can be fitted by an auto electrician so the battery remains charged or you can recharge it yourself with a battery charger.
The water will then have to be pumped through hose, so a hose reel is neccessary.
Then of course, you will need a water fed pole.