Originally invented for foal's diarrhea, it's the best product I have found so far to keep horses' hind ends clean when they suffer from fecal water syndrome or diarrhea.
Instructions per manufacturer: Just spray it on twice a day without washing off the manure first. It will fall off after a while.
Perfect to use when it's too cold to bathe or when you are at a show and have a nervous horse on your hands.
I tried it over the winter on my retired paint gelding with chronic diarrhea who gets sores from all the scrubbing. It worked like a charm and his hind end looks cleaner and healthier than in a long time.
 
UPDATE: Now in summer it seems to work well when sprayed on once a day. With the shorter coat the diarrhea won't get caked in as much as it stains the coat. I noticed that it comes off much easier than before with the hose, no soap or scrubbing needed. Caked in spots still fall off on its own, even the ones in the tail.
Only downside: It takes quite a bit of spray.
 
CANADA customers: We ship to Canada, however, it's very expensive and currently takes forever. You also might have to pay customs on top of everything.