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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.

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That tube provides water to refill the bowl. Without it, you'd only refill the tank.

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During the flush, the siphoning action through the trap pulls more water out of the bowl than is necessary to maintain a water seal, the water is replenished by the bowl refill. Plus dry bowls = sticking contents = partial flush = multiple flushes = wasting more water. – Fiasco Labs Jun 29 '14 at 15:05
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More to the point, the water in the bowl is responsible for blocking sewer gases in the drain line from reaching the room. If the bowl were left empty after a flush, the room would likely get very stinky. – supercat Oct 18 '14 at 12:46

The overflow tube leads to the bowl. It prevents the tank from overflowing, by directing extra water to the bowl.

Nothing prevents the bowl from overflowing, other than the fact that once the water level reaches a certain height the toilet flushes. If the toilet is clogged, the bowl can overflow.

If that tube didn't spray water in the overflow tube, the tank would have to fill all the way and then trickle water down the overflow and into the bowl. However, then there would be no way to stop this prosess, and the toilet would run continuously.

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The refill tube goes into the overflow tube and that water fills the bowl after each flush.

However, the original poster is correct that a lot of water is wasted because once the bowl is filled with water to a certain line and if the tank isn't filled yet, the refill tube will keep flowing and the additional water added to the bowl via the overflow tube simply trickles goes down the siphon.

I guess they could add a feature to restrict the refill tube flow but that would add costs to the mechanism and make it more complicated.

What you can do is simply position the refill tube over the overflow tube so that some will go into the refill tube and some will go into the tank.

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To add to some of the other answers, yes, the tube is designed to drip into the overflow tube.

However, if the spray tube goes too far down into the overflow tube, it can siphon water from the tank. It took a long time to realize this is what was happening to mine, as all components were new and functional. I just had to back the spray tube further up the pipe so that it would still drop properly. Fixed the siphoning and therefore eliminated the wasted filling.

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