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With each flush, much water goes through the toilet refill tube and down the overflow tube. I measured it today and it was 6 cups for one flush. The first cup is certainly wasted because the flapper is up while the water is spraying into the overflow tube.

1.5 quarts per flush seems like a lot of wasted water in my house alone, not to mention nationwide and worldwide.

What approaches might I try to reduce the amount of unneeded water directed down the overflow tube?

Update: I just moved the refill tube so that all the water is redirected into the tank and none into the overflow tube. That saves about 1.5 quart per flush. The toilet seems to flush just as before. The water level in the bowl is unchanged. It seems not all toilets need the extra water that the refill tube directs into the bowl, but all flushing mechanisms of this type assume there is such a need.

Update a few weeks later: The water from the refill tube works in two ways. It contributes to the water that flushes the waste and also contributes to the clean water that remains in the bowl after the flush. When I redirected the refill tube in one toilet, the toilet did not flush effectively. The water in the tank was an inch or so below the manufacture's line. So I will adjust the tank float so the toilet flushes correctly but save the water that exits the refill tube while the tank is refilling.

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    Keep in mind that the overflow tube is only an overflow tube for the tank, not the bowl. The water you think is being wasted is filling up the bowl. If you reduce that too much, you'll spend the money you might save on air fresheners.
    – JACK
    Commented Aug 9, 2022 at 16:47
  • @JACK Not so. The bowl fills the same amount either way, or very close to the same amount. Try it and tell me what you find.
    – Yehuda_NYC
    Commented Aug 14, 2022 at 1:51
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    That actually depend on the toilet and when the flapper goes down. My bowl is almost empty when flapper goes down. If i divert the water from the overflow tube, bowl stays almost empty.
    – JACK
    Commented Aug 14, 2022 at 12:04

3 Answers 3

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There exist devices (mostly just clamps that pinch the hose partially shut) allowing you to control the volume of water flowing through the refill tube. With trial and error, you can reduce the amount of water until the bowl is just full.

Refill tube with roller clamp

On a side note, I would argue that the first cup is not wasted, it is contributing to the volume of water being poured in the bowl that is necessary to achieve a flush. If more water than needed is being released while the flapper is up, the level in the tank can be lowered.

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  • Have you ever seen any problem that resulted from too little water going down the overflow tube? (See update to my original posting.)
    – Yehuda_NYC
    Commented Aug 9, 2022 at 17:14
  • @Yehuda_NYC sometimes the bowl will not be fully re-filled after flushing, if too little water goes down the overflow from the refill tube. Having this problem or not probably depends on what type of toilet you have, and how much water is used for the flush.
    – izzy
    Commented Aug 9, 2022 at 18:11
  • It seems to me that the need for the extra water from the toilet refill tube is toilet specific. I've tried it now with 3 toilets in my house and all 3 work just fine without any water from the refill tube going down the overflow tube.
    – Yehuda_NYC
    Commented Aug 9, 2022 at 19:13
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A misconception - the water is wasted. Reality - that water is to refill the bowl after the flush. As noted by @Izzy, any water that goes while the flapper is open is contributing to the flush volume, and if the flush volume is excessive, you can reset the tank level lower. Otherwise it wouldn't be there. In general, there should be an adjustment on the tank fill valve for how fast it flows.

Unless you already have a seriously water-conserving toilet, the best thing you can do to save toilet water (rather than fussing over the refill tube) is to junk your old toilet and install one that is built, from the ground up, on sound hydraulic engineering to be a low water use toilet. Early "water conserving" toilets were generally lousy modifications to toilets designed to flush with 5 gallons or 3.5 gallons. They often required multiple flushes, thus defeating the conservation.

New ones (as a class, specific examples may not meet this) have generally been properly designed and actually manage to flush on 3-5 liters, though you can still get ones that purport to be conserving at 6 liters per flush or more. They are better than a 2.5, 3, 3.5 or 5 gallon-per-flush toilet, but they are not state of the current art in water conserving toilets. Locally, I found nominal 5 liter/1.25 gallon per flush toilets easy to come by a couple of years ago, while 3 liter/0.8 gallon per flush units were not actually available anywhere in reasonable driving range, despite being claimed to exist. Plenty of 6 liter/1.6 gallon per flush toilets were still on the market as well.

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  • I just moved the refill tube so that all the water is redirected into the tank and none into the overflow tube. The toilet seems to flush just as before. The water level in the bowl is unchanged. Have you seen any problem that resulted from such a change in refill tube placement?
    – Yehuda_NYC
    Commented Aug 9, 2022 at 17:09
  • Are there flushing mechanisms that do not have a refill tube that sends water down the overflow tube with each flush?
    – Yehuda_NYC
    Commented Aug 9, 2022 at 17:11
  • A water-conserving toilet is a great idea but it takes time and money. Moving the refill tube so it empties into the tank rather than the overflow tube costs nothing and takes less than 60 seconds.
    – Yehuda_NYC
    Commented Aug 10, 2022 at 23:17
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Our utility company handed out water saver kits at one time which included this device called a 'diverter' (blue):

enter image description here

Some of the water flows back in the tank and some down the tube.

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