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Question DetailsAsked on 9/20/2016

washer taking water from adjacent toilet tank

Well water with lots of iron which has over years accumulated in toilet tank,. While running clothes washer observed water level in toilet tank went down...vacuum somewhere?

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1 Answer


My guess for cause - low (typically below about 20-30 psi) well pump pressure so when the washer runs it draws water from all the pipes, creating a partial vacuum in the other pipes - so might be pulling from not only the toilet tank but might pull air from other faucets too. This low pressure would relieve pressure on the tank fill valve so it would not seal as tightly in its seat, allowing backflow to occur. Commonly when this is happening you will get air bubbles in the lines and toilet tank when water first starts running, as pipes fill back up after having been drawn down by a major (washer commonly) or lower-level demand in the house.

Is siphoning water out of the toilet tank - could be the water level in the tank is set too high so the air-breaker is under water, because it should not backflow. Could also be the fill valve in the toilet has a weak spring or a buildup of iron algae on the fill valve so it allows backflow, though if due to buildup on the valve seat toilet would probably constantly run a bit too.

You would probably need to replace the fill valve in the toilet tank to prevent this - and can reduce its incidence (though gaskets and seals in the tank tend to go out maybe 2-3 times as often) by using the chlorinated toilet tablets. Usually minimum service charge (typically about $75-150 except in a very few very high cost urban areas) plus about $15-30 parts - or not very tough DIY job IF the shutoff valve at the wall behind the toilet will shut all the way off AND does not leak around the stem after it has been used for first time in probably many years.

Answered 4 years ago by LCD

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