One of those soap dispensers might be good like on a pressure washer?
I was wondering other day, i cleaned a GLASS roof, i used their tap first to get worst of it off, it was a big roof quite messy. Finished and thought ill clean it off with some pure now, well went inside they were spotless??? Rinsed very very well. I didnt test their water, maybe it was very low. I think its all got a lot to do with the rinse in any case.