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.
That tube provides water to refill the bowl. Without it, you'd only refill the tank.
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.
FluidMaster sells a kit to replace a flush valve. One of the components that I had not seen before was a roller valve you slide onto the black tube that allows you to control the amount of water entering the bowl during the flush. I have high water pressure where I live and after flushing, water would drain out of the bowl for 15 seconds to get down to the proper level. To adjust the valve, you flush the toilet, wait till the excess water drains out of the bowl, use a marker to place a small line to mark the optimal water level on the bowl, then use the flow control valve on the (black bowl refill tube), to reduce the flow as needed to only fill the bowl to the optimal level. Fluidmaster sells this tube and valve separately at Home Depot Model # 215 (Store SKU #427596) for $2.99.
The overflow tube leads to the bowl. It prevents the tank from overflowing, by directing the 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, there may or may not be enough water left after a flush to seal the passage in the bowl and prevent gas in the pipe from being released into the room.
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.
1 water goes to the overflow tube thru the refill hose to refill the toilet after flushing , this is to keep sewer gas from entering the room and to prepare for the next flush. 2 At the same time water comes from a different part of the fill valve to refill the tank , all water flow stops when the float level is reached. Yes sometimes the refill tube adds more water than the bowl needs to reach its flushing point which is a waste of water, i would like to have a small valve on the refill hose so i could adjust the flow.
After each flush the water replaces itself already in the syphon constructed down in the bowl, a so called "swan neck", so there is no need at all to put extra water in there. Or do you need an additional tube under your zink in the kitchen to prevent odor from the sewer in your kitchen?.... no! In my eyes its totaly sinless and designed to waste water. Not to mention the additional costs of the syphons and the rubber flaps which need to be replaced every so many years (2-4yrs), designed for ripoff. Measure once the amount of water what you waste putting in the sewer, you will be amazed. There are some manufacturers who sell to their new syphons for the tank little valves which you put on the rubber hose to reduce the waterflow in the overflow tube. I prefer putting a cablebinder over the looped hose to prevent wasting water or to put a 90 degree angle hose so that the water coming out of the hose goes into the tank. In several countries i`ve been you still find the traditional floater ball in the tank where there is no tube going nowhere in the overflow tube.
