I did my two earlier this year with NikWax Rug Proof. I first soaked them in a dustbin overnight, then scrubbed them with a very small amount of liquid soap and a yard broom. Thorough rinse, then treated them with the NikWax and left to dry.
One bottle did both 5'9" rugs with some to spare.
I did all mine myself this year using Nikwax Rug Wash and Rug Proof. Soaked in a big plastic field trough, scrubbed with a soft brush and sponge, kept rinsing until the water was clear. Then proofed and hung in sunshine to dry.
Same as Buddy's Mum. Seems Nikwax is the stuff of choice. I did notice the other day that the water was dripping off Chloe's rug, whilst other horses around were drenched, so it is worth doing.
I do mine with a tent reproofer/water sealant. Either in an old spray bottle or just painted on. It dries very quickly & doesn't smell too much. I did try Nikwax in my washer but tbh didn't find it all that clever. I put it down to it maybe being a bit of a squeeze in the washer & so it wasn't getting on all the rug. They were only 5' rugs at the time though & I'm currently washing 6' s in my washer xx