I have a Fluidmaster (400UK) ballcock in my cistern. I want to use a rainwater tank to fill it just using gravity. The tank's 3 or 4 feet higher but the water won't run in. I've read in this question (https://www.askmehelpdesk.com/plumbing/toilet-cistern-slow-fill-350059.html) details on how to replace the washer, and I've taken mine apart. But there seems to be a very small pinhole for the water inlet. If I make the hole in the washer bigger then it won't shut off when the float rises? Any ideas? Thanks

Do u get water with to cap of ballcock removed?

My guess is that u have sediment from rain water clogging line.

Are u filtering water between rain tank and toilet? If add filter to system, may solve problem.

Good luck

Chuck

I want to use a rainwater tank to fill it just using gravity. The tank's 3 or 4 feet higher but the water won't run in
Even at 4 feet elevation your head pressure's only 1 3/4 PSI. Ballcocks are designed for a higher pressure and if you open up the hole in the washer all you're going to do is destroy the washer. Tie the ballcock into house pressure. Good luck, Tom

Hi Tom

Thanks for getting me straight.

Chuck