For several days I've been hearing a constant trickling from my toilet, with the tank refilling every once in a while. I suspected a leaking flap valve, but on inspection today found something much weirder. Water was leaking out the end of the overflow hose into the bowl, but that water coming from the tank, not the wall. (Eventually, when the tank got low enough, the wall would kick in and refill).
So, faulty fill valve, right? Probably, but here's what's weird. I noticed that if, while it was leaking, I lifted the fill hose up a bit so that it was not engaged quite as deeply in the overflow tube, the leak would stop. Weirder still, if I then dropped it back down, the leak would not start back up again (until a new flush cycle). So I devised the super cheap "fix" below.
The loop just prevents the hose from engaging too deep into the tube (which I admittedly could have also accomplished by simply trimming the hose... although this way it is reversible). I've tested it several cycles now and it is no longer leaking at all.
I am fully stumped. My first guess was this was related to a pressure differential somehow, but the overflow tube is empty, so the end of the hose is in open air whether it is 25% engaged into the tube (as it is now with my "fix") or 50% engaged (as it was before I "fixed" it).
So, just out of good old fashioned academic curiosity... any ideas WTF is going on?