How to empty a swimming pool with a bottom drain?

How to empty a pool with a main drain?

To maintain your pool, you sometimes need to replace some or all of the water. A partial drain should be done in spring if the water no longer tolerates chemicals. It can become saturated; we recommend asking our pool experts via support@foudebassin.com

On the other hand, a full preventive drain should be carried out once every 3 years. This regularity helps prevent your pool from becoming polluted over the long term. Today, we will see how to empty a pool with a main drain. We will cover both natural pools and chlorine pools.

What is the role of a pool main drain?

The main drain is a filter located at the bottom of the pool. Generally made of ABS or PVC, this filtration grate is attached to a hole connected to the water pump. The material of this part must withstand maintenance products such as chlorine and descalers. Likewise, it must support the weight of swimmers. To prevent any accidents, equip it with an anti-suction device such as the Anti Vortex system, for example. Finally, the main drain allows the water to be drained and purified.

But… how do you empty a pool with a main drain?

Emptying a pool with a main drain: user guide

Water quality must be maintained for health reasons. Indeed, stagnant water can develop harmful microorganisms. Optimal purification reduces the risk of bacterial infection. This is why 1/3 of the water should be replaced once a year. Likewise, it is recommended to replace it completely once every 3 years.

Replacing your pool water will also allow you to maintain the lining and sealed parts of your pool. This action helps remove toxic substances that damage the pool walls and bottom. Limescale, algae, and organic matter are removed with the dirty water during each drain. Your pool's tiles or liner will be easier to clean (before the dirt becomes embedded).

When should you really drain your pool?

The guidelines given above (replacing one-third of the water every year, draining completely every 3 years) are rough estimates: the right time depends mainly on the condition of the water. Water that no longer responds to treatments despite proper testing, water saturated with chemicals over the seasons, or a bottom or walls that are constantly getting dirty: these are all signs that justify replacing all or part of the pool water.

Conversely, cloudy or green water cannot always be fixed by draining. First, measure the pH and disinfectant levels and check the condition of the filter: in many cases, rebalancing is enough, and you will save several cubic meters of water. To understand what is settling at the bottom, our guide on pool deposits and sludge can help you.

A full drain is also an opportunity to thoroughly clean the lining, inspect sealed parts such as the main drain and its fittings, and spot any potential leaks.

Before draining: the checks that prevent unpleasant surprises

A pool full of water is stable. An empty pool is not always. Before opening the valves, take a few minutes to check these points.

• The water table (in-ground pool). If the ground is waterlogged after heavy rain or if you are in a wet area, the pressure of the groundwater can lift or deform an empty pool. If in doubt, ask a pool professional for advice before draining completely.
• The weather. A liner left exposed to the sun or extreme cold can shrink, wrinkle, or tear. Choose a mild, overcast period, and plan to refill without delay.
• The pump. It should never run without water: monitor the level during draining and stop it as soon as the water approaches the main drain. To finish draining the last few inches, a submersible pump such as a sump pump is safer.
• Cleaning equipment. Prepare the skimmer net, brush, and telescopic pole in advance: an empty pool should remain empty for as little time as possible.

Where to drain the pool water?

Treated pool water is not like ordinary water: it contains disinfectant and sometimes other maintenance products. The rules are set locally, so check with your local town hall before choosing.

If the water is going into the garden, first give it time to lose its disinfectant: stop the treatment a few days before draining and check with a test strip. A chlorine and bromine neutralizer can speed things up, according to the instructions. Avoid discharging chlorinated water into a ditch, stream, or pond, and do not send it to a neighbor or onto a public road.

Even without disinfectant, the flow rate of a full drain is significant: spread the draining out over time so as not to saturate the soil, as mentioned in step 1 below.

So, what steps should you follow to empty a pool with a main drain?

Step 1: Follow the regulations

Before draining your pool, check if your plumbing system is connected to the sewer system. If not, you must follow your local town hall's regulations. Draining is then done into the public wastewater system. Otherwise, draining the water into your garden may be a solution. But you must ensure with your neighbors that there is no risk of damage or flooding.

Step 2: Perform the drain

The main drain makes it easy to drain even if the bottom of your pool is flat. Simply proceed as follows, from the area housing the pool pump:

• Stop the pool pump;
• Close the skimmer valve;
• Set the filter valve to sewer;
• Open the main drain valve;
• Set the multi-port valve to drain so that the water drains without passing through the hydraulic system's filter;
• Turn the system back on to start the draining.

Step 3: Clean the pool

To clean a partially drained pool, use a skimmer net to remove large debris from the surface and bottom. Then, use a pool vacuum brush to scrub the walls and bottom of the pool. The waterline sometimes leaves a yellowish mark all around the walls. This is a buildup of algae that you can remove with a soft brush and baking soda. It is advisable to remove this yellowish band as soon as it appears.

When the pool is completely empty, you can brush its walls and bottom with a telescopic pole. To remove stubborn stains, apply baking soda and scrub with a sponge. Rinse all impurities with water and drain the pool again. It is better to avoid using toxic chemicals as a safety precaution.

Step 4: Refill the pool

To refill your pool, opt for high-quality water. City water is perfectly suited for this purpose because it is already treated. However, its cost remains quite high and varies from region to region. If you have a well, you can use its water. But it must be tested and treated before use. This can be costly. Finally, add chlorine to the skimmers of your filled pool and run the filtration for 12 hours.

After draining: refilling and initial settings

Refilling is when the quality of the season is determined. Refill continuously while keeping an eye on the level, up to the skimmers' useful height, then set the valves back to the "filtration" position.

1. Refill and restart the filtration. Allow 12 hours of filtration, with chlorine in the skimmers, as indicated above.
2. Measure. Check the pH, alkalinity, and disinfectant levels with pool test strips, especially if the water comes from a well.
3. Correct in order. First rebalance the pH and alkalinity, then adjust the disinfectant level by following the instructions for chlorine pool products.
4. Prevent limescale. A descaler distributes and fixes the limescale in the new water; it is dosed according to the product instructions.

If you do not drain your pool for the winter, a non-foaming winterizing product helps limit the proliferation of algae and bacteria during the cold season. For an in-ground pool, it is therefore often preferable to leave the water in the pool and winterize it rather than draining it: ask a pool professional for advice on your type of pool.

You can also find our selection of pool winterizing equipment.

There you go! You know how to fully enjoy your pool with clear and limpid water. You just need to drain it at regular intervals. ⅓ of its water should be replaced at least once a year and completely once every 3 years.

To learn more about the maintenance and landscaping of your pool, check out the other articles on our blog!

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