IF your water tank is kept out of the light, there is no reason to change the water at all, just add to it. I clean mine once a year in the fall. And yes you don't want it air tight like the gravity waterers. If THEY aren't air tight, all the water will run out. With nipples, there must be a way for air to replace the water that is being used.
Replace the leaking nipple.
My coop is a 10'x12' converted horse stall. Like @aart I don't change the bedding in my coop often, when I do I rake it out into the barn alley which is the girls' indoor run. Unlike @aart I don't have a poop board, I just rake through under the roosts every morning. I add some pine shavings on occasion, I use maybe 4 bales a year.
Replace the leaking nipple.
My coop is a 10'x12' converted horse stall. Like @aart I don't change the bedding in my coop often, when I do I rake it out into the barn alley which is the girls' indoor run. Unlike @aart I don't have a poop board, I just rake through under the roosts every morning. I add some pine shavings on occasion, I use maybe 4 bales a year.