How to Drain the Water from a Sand Filter

As you start to plan for your pool winterization process and any off-season maintenance, you’ll want to take a look at your sand filter. While the sand may not need to be replaced every year, if temperatures are cold enough to freeze during winter, you’ll need to drain the water from your filter.

Let’s examine the reasons to drain the water from your filter and how you should do it.

pool pump and equipment
Draining water from a sand filter

Why Drain the Water from a Sand Filter?

There are three reasons that you need to drain the water from your sand filter:

  • Winterization or shutdown
  • Sand replacement
  • Filter repair

Keep in mind that if you have a DE filter, or cartridge filter, you’ll need to drain these filters too for repair or winterization. The same principles apply to draining these filters.

Winterization of a sand filter requires you to remove water from the filter so that it does not freeze during colder temperatures. If water stays in the filter and freezes, it can expand in the filter housing and cause it to crack.

Water in the filter during colder temperatures can also damage the multiport valve or the pipe unions.

Sand replacement should occur every 3-5 years to keep it working optimally. Over time, the sand particles wear down and lose their rough edges. When this happens, the sand cannot filter out particles as effectively.

Filter repair of the laterals, for a sand filter, or the grids, for a DE filter, will mean the filter should be drained. In the case of a sand filter, the sand will need to be removed so you can access the parts inside the filter.

Step by Step Guide to Draining the Water from your Filter

  1. Check your pump timer and make sure it’s turned off
  2. Find the drain plug on the bottom of the filter
  3. Remove the plug and allow water to drain
  4. Connect a hose to the drain plug (if desired)

Step 1. Turn Off Your Pump Timer

You want to make sure if your pump is on a timer or an automatic setting that it gets turned off. Otherwise, you run the risk of the pump turning on while you’re draining the water. If that happens you can burn out the motor on your pump, so don’t overlook this step!

Not to mention the fact that you’ll have water going everywhere if you’ve opened the drain plug or have disassembled the filter in any way.

If you’re unsure where the timer switch is, you can always disconnect power to the pump itself.

Step 2. Open the Drain Plug to Release Pressure

Locate the drain plug at the bottom of the filter. You’ll need to turn it slowly in a counterclockwise direction to release any pressure that has built up.

Some filters also have a pressure release valve. You may open this too.

Step 3. Remove the Drain Plug Completely

Once the pressure has been released, you can remove the valve to let the water drain. Be sure to put the drain cap in a safe spot so you can replace it when you’re ready to refill the filter.

Some filters have a dual drain plug, so if no water is draining, you’ll need to check for the inner valve to make sure it is open as well.

Step 4. Connect a Hose to Direct Water Runoff

If you need to drain the filtered water away from where your pump is located, connect a pool hose so that you can direct water to a safe area.

Milliard 50 ft Heavy Duty Backwash Hose, Great for Water Disposal - Weather and Chemical Resistant - 2 inch Diameter

NOTE: The hoses are sold in different lengths, so be sure to measure the distance from your filter to where you need the water to go before you purchase one.

Required Tools

There are normally no tools required to open the drain. In most cases, you can turn the drain by hand. But here are a few items that may make your job easier if you’ve got them on hand.

If you need to loosen any of the pool unions to relieve valve pressure to open the drain, a pipe wrench or some PVC pliers might be useful.

DURATECH 4-Piece Heavy Duty Pipe Wrench Set, 8",10",14",18", Adjustable Plumbing Wrench Set, Malleable Cast Iron Handle, Exceed GGG standard

Channellock OF-2 2 Piece Oil Filter & PVC Pliers |12-Inch & 9-Inch | Ideal for Engine Filters, Conduit, and Fittings | Forged from High Carbon Steel | Made in the USA

Depending on the location of your pool, you may wish to use a hose to direct the filtered water to a specific area of your yard.

How Long Will it Take to Drain the Water?

The exact time will depend on the size of your filter, but the water should be completely drained within an hour. You can leave the plug out for longer than that to allow the sand to dry out more if desired.

When changing the sand out, you might want to allow the sand to dry longer so it’s not as heavy when you go to remove it.

What Do You Do if the Water Won’t Drain?

Be sure that there isn’t a second, internal drain cap that needs to be opened. Some filter models have a two-part drain plug.

Release the Pressure

Since the filter system is a closed system, sometimes you may need to release the pressure from the top of the filter so that water will flow. This can be done by loosening the unions on top of the filter if opening the drain plug did not release enough pressure.

Remove and Clean the Screen

There is also a screen inside the drain plug that keeps sand from draining with the water when the plug is open. It’s possible that the screen is blocked by particles that won’t allow the sand to drain. Unfortunately, this piece is difficult to clean or replace without first removing the sand.

How Much Water Do I Add to Refill my Sand Filter?

If you have not replaced the sand in your filter and are just re-opening the pool for the new season, you do not need to add any water. When turned on, the pump will push water into the filter.

If you are replacing your sand, you’ll need to fill the filter between ½ to ⅔ with water before adding sand to protect the laterals from being damaged as the sand is added.

What Do I Do if I Lost the Drain Plug?

The drain plug is necessary to keep water in the filter. If you lost it during the off-season or just need to replace it because it’s worn, you can order replacement plugs.

Waterway Plastics 806105406750 Drain Cap Screen Sand Filters

Make sure you get one that fits your brand and model of pool filter.

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