I found that nipple waterers stayed cleaner because they have a lid over them. (Make sure it isn't air tight, or the water won't flow.) I put a couple tablespoons of kombucha tea (per gallon) in the water, and had no issues with slime. I emptied, cleaned, and refilled them every 2-3 days.
If you don't have kombucha, a bit of cider vinegar will work. The acidity slows down the slime growth. I like the kombucha for the probiotics in it.
If you don't have kombucha, a bit of cider vinegar will work. The acidity slows down the slime growth. I like the kombucha for the probiotics in it.