I've been using a gravity feed system on 6 different racks (about 100 valves) for about a year now and my only two issues have been the occasional flood (about 4 in a year) and a clogged up filter once restricted the flow to the point I lost a handful of rats due to dehydration. That was a hard lesson to learn ...now I simply check the filter atleast twice a month. The only other issue I've had isn't directly a flaw of the watering system but has got me in trouble twice was loose rats chewing through the water lines and flooding the bins below. I've seen others plumb their system with PVC pipe and use screw in fittings but I'm going to stick with the flexible hose due to price and ease of installing/replacing. I've since managed to avoid this issue by simply installing 2 live traps to catch them before they do any harm.