This is giving slightly mixed messages. Do you mean you own the pitch? or are you renting it.?
My assumption is you are renting, and thus the owner of the land may have view about how you drain the system.
Foul water ( i.e toilet ) must only be disposed of down the Foul disposal point.
Grey water (i.e. water that has any additional contamination other than foul water) should be disposed of in a designated discharge point.
Some sites may have specific instructions about the discharge of clean cool water ant they should of course be followed, but in the absence of instructions or advice from the site staff, there is usually not a problem with discharge as you tow away.
But if your not moving, so all the water is discharged in one place . the site might be concerned about water logging or creating a mud bath. It might be worth thinking about getting a long shallow garden tray to collect the drain down water, so you can move it and dispose of it safely. Such trays are also useful for standing dirty boots and shoes in when you not draining the water system.
