plumbingtoilet
I can easily understand the purpose of the overflow tube itself, but why is the little black hose that comes from the fill valve placed down into the overflow tube? On my toilet, there is a strong stream of water that comes from the black hose, and it seems like going right into the overflow tube is a complete waste of water.
I know I must be missing something obvious, but I can't see it.
I think @Tester101 has asked the pertinent question: Is the fill valve height adjustable? It is. You need to adjust its height:
The overflow tube drains directly into the bowl, not the tank. The only way I can think that it would prevent the tank from filling is if it was cracked or had a hole in it and allowed tank water to drain into the bowl. If this was the case, you would notice the fill valve cycling if it was a slow leak or never shutting off if it were a large leak. The reason the tank fills quickly when you divert the bowl refill tube into the tank is that you are simply not splitting the water from the fill value between the tank and bowl any more.
It sounds like your fill valve assembly is the problem. The fill value has 2 outlets, one that directs into the tank, and the other that sends water into your bowl refill tube. My best guess is that something inside of the fill value got clogged with sediment, hard water deposits, or something else that restricted it. These are relatively cheap to replace and likely not worth the time to clean them out in my opinion.
Best Answer
That tube provides water to refill the bowl. Without it, you'd only refill the tank.