Swimming Pool Blog

How to Safely drain your swimming pool

How to Safely drain your swimming pool
by Rob Cox, March 23, 2011

How to safely drain your in ground or above ground swimming pool

Subject: Changing pool water - rb63 posted this in our Pool Talk discussion forum recently:

pool talk discussion board post about how to drain a swimming pool

I told our member that he might want to take a look at a recent blog post on acid washing a pool safely, which had information about properly draining a swimming pool. This gave me an idea for a new post on the topic, focusing on how to best drain many different pool system types. Draining a pool or partial draining becomes necessary to correct poor water quality, or when making extensive pool surface repairs.

Many localities, cities and towns have laws in place regarding when, where and how you can drain a pool, or even discharge pool water. Check with your local Building & Zoning division of your local government for any restrictions on swimming pool draining. The following pool draining tips apply for all pool types - specific information on draining in ground pools and how to drain an above ground pool, are below.

General Pool Water Draining Tips:

  1. Make sure that chlorine or biguanide (Baquacil) levels are near 0.00 ppm. Adjust the pH to within 7.2-7.8.
  2. The best location would be into a storm drain, headed for water treatment plants. If not possible:
    • Pump to an open area, far from the pool, to keep the water from coming under the pool.
    • Avoid pumping into creeks or streams, to protect local wildlife and watershed.
    • Avoid drowning vegetation, brush and small trees in pool water.

In Ground Pool Draining:

  1. Important to pump your water far away from the pool. Too much hydrostatic pressure under a concrete pool can lift it out of the ground, and smaller amounts can come up under pool liners, and cause the liner to bulge into the pool. Pump your pool water the furthest point possible, and consider the topography surrounding the pool - avoid depressions, low spots or poor drainage areas. Monitor your pumping to ensure that erosion or over-saturation is not occuring.
  2. Concrete pools have several 1.5" hydrostatic relief plugs plastered into the floor centerline. Usually there are 2 in the deep end also, and another one in the main drain pot. As the water is being drained, chip the plaster away from the white pvc plug, and use pliers to unthread it, counter-clockwise. This will allow water that is beneath the pool shell to come into the pool, if any exists. Always remove these plugs as you drain the pool. Leave the plugs removed until you are ready to fill pool, then seal them back tightly. Vinyl liner pools do not have these hydrostat plugs.
  3. Vinyl liner pools being drained for water problems should lower only as far as 6" above the floor. If you go lower, the liner will relax and need to be reset to avoid wrinkling. Draining vinyl liner pools completely also has the risk of floor damage, liner failure and even partial wall failure, if any are old, weak and near failure.
  4. If you have a Sand Filter or a DE Filter, you will simply roll out your backwash hose, and set multiport valves to WASTE or if you have a push-pull slide valve, you will simply backwash your pool all the way down to the main drain. Before the water gets below the skimmer, you will need to close the Skimmer valves so that all the water is coming to the pump from the main drain only.
  5. If you have a cartridge pool filter - there is no valve to backwash with, unless one was purposely installed for water level adjustments. A tee fitting or a valve can be installed before or after the filter to allow water to exit the system, or a small submersible pump can be used to drain the pool.
  6. If you have no separate valves, but only one pipe coming into the pump, then you have what's called "Combination Skimmers," where the main drain is tied to the skimmer, underground, and one pipe goes from skimmer to pump. If you see one hole only in the skimmer center (under the basket), you can continue to pump the pool nearly empty by plugging the top of the skimmer with a #10 expansion plug, or threaded plug with o-ring. If you see two holes, usually pool side, deck side - then it is more difficult to pump below the skimmer. The easiest method is to connect a tightly sealed threaded hose adapter into the hole which draws to the pump, and connect a primed, "tight" vacuum hose to it. If you hear air sucking, you may need use some tape or sealant.
  7. Don't shut off the pump once you get it lowering below the skimmer, or you may lose prime and have trouble getting the water draining again.
  8. Keep an eye on the pump and the discharge throughout the process. Depending on your pump size / pool size, this can take 4-8 hrs.
  9. Work fast on the pool, it's best not to leave plaster or vinyl exposed for long. Begin refilling the pool as quickly as you can.

Above Ground Pool Draining:

  1. Above ground pools typically have one pipe (hose) out of the pool, and one hose returning to the pool. Because there is no main drain on most aboveground pools, you will only be able to lower the water to the bottom of the intake or skimmer, using your aboveground pool filter system.
  2. To drain an aboveground pools, either a). Use small submersible electric pump and garden hose, or b). Start a siphon with your vacuum hose / head on the pole, or a siphon using a few garden hoses.
  3. Pumping the water far from the pool's edge is best, so as not to oversaturate the soil supporting the pool.
  4. Monitor the draining and the discharge. Siphoning can take days, a small submersible pump will take 6-12 hrs.
  5. Work fast to clean the bottom if needed, and re-fill the pool as quickly as possible.