One horse cleans the tanks for herself and her friend. She plays in her water and leaves a handful of sand and pebbles in the bottom and all that pawing and splashing keeps her tub scoured out. Usually, the 40-gallon tub will be almost empty at feed time so the barn hands dump out her filthy sandy dregs and refill. I always tell them to just fill it half full since she wastes so much but they often top it off. In any case, she gets clean water twice a day and has an auto waterer on the fence as well. I had purchased nice and expensive stock tubs but she damaged hers playing with it, causing it to leak, so I had to switch and use her metal stock tub for hay and her rubber tub for water and play.
FWIW, I asked the clerk at the feed store what was better about the galvanized tanks as they were much more expensive than the rubber tubs. She told me they were easier to clean. I found that to be true. I can get them really clean with the “jet” setting on my hose nozzle, so much easier than the rubber tubs!
With the other two horses who still have a big rubber water tub, I put in a few handfuls of soil, mostly decomposed granite pebbles and large sand, and I scrub the tubs with that and a rag or brush, then power wash. The power wash on my hose is not powerful enough by itself to clean the rubber tubs.
