IMHO, don't bother with a brush and detergent pellet. Soak the car with
the hose then use a bucket and sponge using car shampoo from the likes of
Halfords - buying it by the 5 litre container makes it pretty cheap.

I prefer the brush and soap pellet. Less work than the bucket and sponge.
But then mains pressure hot water is useful for this...

Christian.