Siphon fill valve

Toilet Tanks Can Backflow

Do you know that toilet tank water can back-siphon into the drinking water supply? If you have older toilets installed in your home, you may be at risk of having a backflow. To find out more about it, read my post.

How toilet tanks work

A tank flushing toilet fills from a fill valve (or ballcock) located on the left inside corner of its tank. A cold water supply connects to the bottom to fill the toilet every time it gets flushed.Toilet tanks are cross connections because the water inside of them becomes contaminated with bacteria and other contaminants.

Through years of fill valve development, there have been many different designs made by various manufacturing companies. Although the models are all different, the primary function is the same. There’s only one type that is accepted and approved by all plumbing codes, and I will get to into that very shortly.

Right and wrong !

There used to be two kinds of fill valves to choose from for repairing a toilet, and they were the following:

  •  siphon (or submerged inlet)
  •  anti-siphon

They both functioned the same except that the siphon type had the potential to backflow. For example, if toilet bowl cleaner was inside of a toilet tank and there was a water main break negative water pressure in the water piping would create a siphon, and the blue water would flow back into the drinking water supply.

Here are recent cases of backflow incidents throughout the United States. This information will help you to understand how dangerous backflow is.

How would you know?

anti-siphone fill valve
Fill valve that is anti-siphon.
Not a anti-siphon fill valve
Fill that siphons.














Referring to the pictures above to determine if you have the wrong fill valve inside any of your toilets all you have to do is just lift the lid off of the tank and inspect the inside of it. If you verify that you have the wrong fill valve in any of your toilets, shut off the water and have it replaced as soon as possible. Don’t wait!

The particular valve in the bottom picture significantly was used throughout the early 1970s and mid-1990s. It’s no longer manufactured or sold in the United States anymore.

Don’t drink toilet tank water

If you’re not sure, your toilets are working correctly or that they’re safe to use. Call Vince an experienced master plumber who has many years of experience identifying and fixing potential cross connections in plumbing systems. Click here to schedule an inspection of you all your toilets and plumbing.

Carbon Monoxide Safety Check

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