In South Africa we had a mobile grooming parlour which would come and wash the dogs etc in the yard (or in the garage in winter).

They had a sort of trailer / caravan thing with drop sides and it was fully kitted out like any other parlour!

It came in really handy with my Rhodesian Ridgeback, Fiona, cos she was too big for me to wash on my own, and she hated going in the car!