I do them myself, after removing as much hair as I can. There are no launderettes in my area! Thinking of going the tub route this time as I'm paranoid about lice and mange and bought some second hand ones. Think I'd like them done in dermolene as a day soak!
I'm not brave enough to take them somewhere non horsey public might smell them!!
But I do was them myself at home, hosepipe (or the jet wash if I can find it!), hands and knees and scrubbing brush. I do the outside first then turn it over and do the inside then hang it on a fence and hose pipe til the water runs clear.
They seem to hold their waterproofing through this (and I've been doing it for 3 years now) but I guess there will be a year when I need to take them for proofing.
I also use fleeces/ summer sheets under rugs and pop those in my old washing machine - gets most of the greese out.
I alternate between prof cleaning with repair and reproof as necessary and cleaning at home with pressure washer and a stiff broom. Works well for me and saves money. I can get summer weight in the washing machine but it doesn't go down well with OH so I wait until he's away!
just check your filters periodically ! my washing machine broke and the filter was blocked with all the moult from the numnahs and fleeces i'd washed over the previous months...... once unblocked it was fine - just check once a month or so