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Photograph of a water pressure tank air valveWater Tank Drain Valve Location & Repair
How to Drain a Water Tank

Water storage tank drain procedure & water tank drain valves:

Where do we find the water pressure tank drain valve on a private well, tank, and pump system, how is the water tank drain valve used during water tank service or repair, and how we replace or repair leaky drain valves.

How to get water out of a water pressure tank or water storage tank. Step by step procedure for draining a water tank and steps to return the water tank to service after draining.

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Water Tank Drain Valve: Guidelines, Usage, Location, Repairs

Photograph of a sketch of the main controls and valves on a water system

Water Tank Drain Valve Location & Tank Tee

Typically the water tank drain valve is located on a brass fitting called a tank tee also showing in our page top photo.

[Click to enlarge any image]

The water tank tee is mounted at the bottom or lower side of a water pressure / storage tank where it provides the following:

Usually when a water tank drain valve is to be opened the water tank drain is connected to a hose which is run outside of the building or to a nearby floor drain.

This water tank drain is not normally opened when the pump is turned on since you'll simply run the pump and flood the building, but we have used it as a convenient way to connect a water hose to the system. We once put out a small fire in this manner.

Watch out: Water tank drains should be piped to a visible location, not installed with a drain to a crawl space as this owner did. For convenience, the owner wanted to be able to drain the water system to avoid freezing when this home in Rhinebeck New York was unoccupied.

But first of all, sending water into the crawl space risks mold, rot, and insect damage to the building, and second, it's generally a bad idea to send any drain, overflow, or relief valve to a hidden location. If the piping is leaking we want to know it.

And finally, as we don't know where the end of that black garden hose (marked with a yellow question mark) terminates we have to worry that it terminates in a pool of unclean water or in wet soil - forming an un-sanitary cross connection that can contaminate the building's water supply.

If the water tank drain is leaking it needs to be repaired (usually a simple internal washer) or replaced.

But you can defer this repair by screwing a garden hose cap onto the gauge threaded outlet. We put these caps on all of our tank drains in areas where children are playing since on occasion they've been opened by curious kids.

Procedure for Draining a Water Pressure Tank

Photograph of a water pressure tank air valve, relief valve and main water shutoff

  1. Turn off the water pump or well pump. Usually this is accomplished by an electrical switch that powers the well pump, usually located close to the pump; if you can't find that switch turn off the pump circuit breaker or fuse.

    Watch out: do not touch electrical equipment if standing on or in water. You could be shocked or killed.
  2. If there is a shutoff valve between the water tank and building, open it. Most water systems include this valve, on piping between the water pressure tank and the building water supply system piping. The valve is usually close to the water pressure tank.

    In our photo above the white arrow points to the main water shutoff valve. When this ball-valve lever-type handle is set parallel to the water pipe the valve is in the open position.
  3. If there is a shutoff valve between the well piping and the water pump, close it. This may help avoiding loss of well pump prime as we discuss below. This valve may not be present on your system as most well and pump systems use check valves but no shutoff valve between the house and well piping.

    This valve is more likely to be present if your water pump and pressure tank are functioning as a water pressure booster for a municipal water supply system.
  4. Connect a drain hose. If necessary to prevent spilling water where you don't want it, connect a garden hose to the water tank's drain valve and run the other end of the hose to a suitable drainage location.

    Ideally the drain hose should slope down continuously from the point of connection to the water tank, but if your hose has to run uphill and then down, as long as the "down" portion of the hose is longer than the length of hose between the water tank and the hose high point you'll still be able to drain the water tank by gravity. The longer downhill hose length will help siphon water out of the tank.
  5. Open the drain valve at the water tank to which you connected the drain hose
  6. Open one or more nearby plumbing fixtures such as a sink or tub faucet to allow air to enter the piping and water tank system. Without allowing air into the system you won't be able to drain all of the water out of the water tank.
  7. Wait for water leaving the water tank to stop. At this point the tank should be empty. Gently rocking the water tank (taking care not to break or disturb a plumbing or electrical connection) can sometimes help confirm that the tank is empty.

If you are unable to get all of the water to drain from the water tank

How To Restore a Water Tank (and pump) to Service After Draining

  1. Close the water tank drain. Yo

    u can also remove the drain hose at this point. Quickly lift up the removed end of the drain hose that you'd connected to the water tank drain to help assure that any water remaining in the hose drains to outside rather than backwards onto the floor at your water tank.
  2. Check or set the water tank air pressure pre-charge.

    For a bladderless water tank that you emptied completely of all water, no air pre-charge will be needed to return the tank to service and adding air will simply push that air out of nearby faucets. If you did not fully drain the water tank

    See WATER TANK AIR, HOW TO ADD

    For an internal-bladder type pressure tank that is empty the air pre-charge is set to 2 psi below the pump control switch cut-in pressure.

    See WATER TANK AIR PRESSURE ADJUSTMENT for tanks that use an internal bladder
  3. Close building faucets that you opened to allow air to enter the piping and tank system to aid draining the water tank
  4. Close the main water valve between the water pressure tank and building water piping
  5. Open the water valve between pump and well piping (or municipal supply piping if this is a water pressure boosting system) if one is present.
  6. Turn on electrical power to the water pump.

    Watch out: if your well pump has lost prime you should not allow the (above ground) water pump to run dry as that can damage the pump leading to costly repairs. A faulty foot valve or leaks in well piping or other problems can cause loss of well prime.

    See WATER PUMP PRIMING PROCEDURE
  7. Wait for the pump to stop:

    the water pressure should rise to the water pressure control switch cut-off pressure (typically between 40 and 70 psi) in a few minutes (less than 5 unless you are using a very large water storage tank system). If the well pump keeps running and never reaches the cut-off pressure, then

    See WATER PUMP WONT STOP RUNNING
  8. Open the main water valve between the water tank and the building.
  9. Open one by one each faucet to purge any excess air from the building piping & water system. T

    hese are the faucets that you had previously opened to let air into the piping system to drain the water tank, then had closed for this step. You will probably see air discharge at the faucet that you open.



    Leave water running until the air discharge stops. If air discharge continues more than a minute there may be a separate problem.

    See AIR DISCHARGE at FAUCETS, FIXTURES

    The pump may turn on during this process depending on the volume of water necessary to remove all of the air from building piping.
  10. When the air purge is complete at each fixture close the fixture valve. The pump may run for a brief period but should stop. If the pump does not stop and all valves are closed,

    See WATER PUMP WONT STOP RUNNING

Your water system should now be operational. What else might be wrong?

In an emergency if your building has lost water pressure but a neighbor's water system is working, you can "back feed" your building's water piping by connecting a garden hose from your neighbor's outside water faucet to this water tank drain.

You'll need a double-female-ended washing machine hose to complete the connection. Of course you could back-feed from a neighbor to any easily accessible hose connection on your building such as an outside water spigot or a washing machine cold water hookup as well.

 

Reader Comments & Q&A

On 2020-07-30 by (mod)

No, Milton, not if you only want to CHECK the pressure in the tank; and draining the water would lower the air pressure or air charge pressure in your tank.

However when you are SETTING the water pressure tank air pre-charge, YES you drain all pressure (and water) from the tank, then set the air pre-charge to 2 psi below the pump control cut-in pressure.

On 2020-07-30 by Milton

To check air pressure do you have to drain the water first?

On 2017-01-22 by Amy

We live right ouside city limits. Which puts us on a private water well. Our cistern is 2500 gallons of holding water. We run water up hill about 200 ft to the cistern. Then we run water to the house about 100 ft. We constantly have a loss in pressure. Also our pressure switch is constantly needing repair.

Fortunately, or for us right now unfortunately. We are having a lot of rain in California. So we are experiencing a bit of problems with our water. Our pump stopped working feeding our water to the house. So we again repaired the switch, the capacitor. We found that the pressure gauge from the cistern to the pump was not workig. So we put a new one on.

he pump itself has been tested to make sure it's not froze. Which it is in great working conditions. So now that we have literally gone through the electrical wiring, and the pump and bladder tank. We still can not get the pump to stop getting hot. It also doesn't stop when the switch is enabled, but gives no water to the house.

Is it my holding tank? We know that water coming out of the cistern. Just not fast. I'm assuming that there isn't a lot of pressure from the cistern itself? It comes out at about 4 gal per min or so. We haven't done a psi test on it. I'm so confused. I need water, lol who doesn't right. Can anyone help please.

Question: water tank air pressure gauge stuck at 30 psi

(Dec 2, 2012) Mike said:
My system looks almost the same as above. Im trying to winterize the system. Drained and blown out with compressed air but the gauge still reads 30 psi. ?

Reply:

Mike,
If you drained the water pressure tank and piping and the gauge still shows pressure, quite probably the gauge is stuck.

Try tapping on it gently, or just replace it.

Question: Should we drain the tank to get rid of any sediment?

(Dec 4, 2012) Diane said:
We have an enormous amount of iron or minerals that stain our toilets red even though we change the filter on the water tank every two months. The water even comes out of the faucets with a red tinge. Should we drain the tank to get rid of any sediment? The water tank is approx. 12 yrs. old.

Reply:

If the stain is from iron not sediment then there may not be much sediment to drain from your water tank.

At WATER TREATMENT EQUIPMENT CHOICES you'll find articles about removing iron from the water supply.

Question: leaky drain valve at sump?

(Mar 6, 2013) Mike M said:
I recently replaced my sump pump and noticed that there is a small trickle of water flowing into the sump basin from my well water tank. It seems this shouldn't be the case. Does this mean that my valve is leaking or is this intended to stay on to relieve pressure? If it shouldn't be happening, then the sump is turning on much more often than it should, not to mention the well pump.

Reply:

(Jan 25, 2014) George Raven said:
You can drain back to the source ( well or place where you take the water)

Question:

(Jan 25, 2014) George Raven said:
I have a well and a check valve what I did is when I shut down the pump I open a valve that bypass my check valve sending the water back to the well.
Easy

Reply:

Looks as if we are mixing up sump pumps and well pumps. Mikes sump pump needs a new check valve.
George's suggestion is interesting bit I'm a bit confused as in the case of a well with an aboveground pump his idea will lose prime.


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