I have these type of water cups, attached to pvc with 2 liter threaded into the line as source. I rarely need to clean them because they are placed about chest high so it's really hard for the birds to poop in them or kick the sand into them.I have two of these (https://www.amazon.com/dp/B01IO9A6RK/?tag=backy-20) hooked up to a gravity-fed system with a 2-gallon bucket and it's working very well so far. The height at which I mounted the line prevents the birds from kicking too much sand into the cups so I just use my index finger to sweep them out every few days and there's never more than a single layer of sand at the very bottom. The birds don't seem to have any problem getting as much water as they need and it will be nice to be able to add ice/frozen water bottles to the bucket during the hottest part of summer around here
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I've been using these cups on vertical PVC tube waterers in my chicken coop and run for years and have had no problems with them whatsoever. Highly recommended!