I would just use a jet wash and a bucket of warm water with some laundry powder in. Then use tent reproofer spray on it afterwards. Simples.
We are lucky enough to have an industrial washing machine and tumble dryer at the yard - I can't imagine life without it now!
There's a girl that comes into the pub where I work that comes straight from the yard - she absolutely stinks! I find it quite vom-inducing and I have a horse so god knows what the other customers must think!