Horsewear say that its rambo turnouts are made from ballistic (sp?) nylon and as such should still be waterproof after being washed. Rhino's would need reproofing though
If you wash them just in plain water then any rug will remain waterproof as long as the temperature of the water does not exceed 40% so a normal wash cycle will be fine. Far cheaper to wash them yourself at the local launderette rather than send them off to be cleaned and re-proofed. Mine come out looking like new after a quick wash at the posh-wash. £6 for the biggest machine and I can fit 4 rugs in there !
I have always washed mine in fairy on a 40 degree was in an industrial machine and have never yet had to reproof any of mine. The one that is 9 years old will get reproofed this year tho