As others have mentioned, carry a 25L container of water and a small bottle of Zoflora which you can buy in supermarket, very cheap and works brilliantly. Chuck the Zoflora in the water, raise the suspension on unit and drop it on the trailer to make a decent runoff slope. Wash down from headboard end then squeegee the lot out. Reset suspension & refill container for next time in case you arrive somewhere you can’t get water easily, especially in middle of night. If heading to load ambient after washing then run fridge at 0 or less on the way to collection point to kill any remaining odour. Switch off fridge as you walk around to open doors before backing onto bay.
I used to run fresh fish and if no onsite wash facility washed out after every run like this, as soon as tipped. Fresh fish after gutting leaves bloody/watery liquid all over the floor after tipping so deffo necessary.
J