How To Drain A Swimming Pool With A Pump: The Technical Professional’s Guide

To drain a swimming pool efficiently, utilize a high-capacity submersible pump positioned at the deep end or set your pool’s filtration system to the "Waste" cycle if using the main circulation pump. This process requires maintaining a discharge rate that prevents motor burnout while ensuring the pool shell remains structurally stable against hydrostatic pressure.

Essential Preparation and Equipment Selection

Draining a swimming pool is a high-stakes maintenance task that should only be performed when water chemistry parameters—specifically Total Dissolved Solids (TDS), Cyanuric Acid (CYA), or Calcium Hardness—have exceeded manageable thresholds. Typically, when TDS levels surpass 2,500 ppm or CYA exceeds 100 ppm, a partial or full drain becomes necessary to reset the chemical baseline. Before commencing, you must identify the structural integrity of your pool and the local environmental regulations regarding wastewater discharge.

Mandatory Gear and Specifications

• Submersible Utility Pump: A 1/2 HP to 1 HP pump is recommended. Ensure it is rated for continuous duty and can handle at least 2,000 to 4,000 gallons per hour (GPH).
• Discharge Hose: A reinforced 1.5-inch or 2-inch backwash hose or a heavy-duty garden hose (for smaller volumes). The larger the diameter, the lower the friction loss and the faster the drainage.
• Power Supply: A Ground Fault Circuit Interrupter (GFCI) outlet is mandatory to prevent electrical shock in a wet environment.
• Chemical Neutralizer: Sodium thiosulfate or a similar dechlorination agent to bring chlorine levels to 0 ppm before discharge.
• Submersible Pump Intake Screen: To prevent debris from clogging the impeller.

Pre-Procedure Benchmarks

• Weather Window: Do not drain a pool if heavy rain is forecasted or if the air temperature exceeds 85°F (29°C) for plaster pools, as this can lead to "popping" (hydrostatic lift) or shell cracking/shrinkage.
• Groundwater Check: Verify the height of the local water table. If the water table is high, draining the pool can cause the entire vessel to float out of the ground.
• Duration Estimate: A standard 20,000-gallon pool using a 3,000 GPH submersible pump will take approximately 6 to 8 hours to drain completely.

Step-by-Step Execution for Pool Drainage

The following procedures outline the two primary methods: using an external submersible pump (preferred) and using the pool’s built-in centrifugal pump.

Step 1: Dechlorination and Legal Compliance

Before a single drop of water leaves the vessel, you must ensure the water is environmentally safe. Most municipalities prohibit the discharge of chlorinated water into storm drains because it is toxic to local aquatic ecosystems.

1. Stop adding chlorine 48 to 72 hours before the planned drain.
2. Test the water using a high-grade DPD test kit to ensure the Free Chlorine level is 0 ppm.
3. If time is a factor, add a chlorine neutralizer according to the manufacturer’s dosage instructions to reach 0 ppm immediately.
4. Identify your legal discharge point. This is usually a clean-out port for your home’s sanitary sewer or a designated area on your property that can absorb the volume without causing erosion or flooding a neighbor's yard.

Step 2: Positioning the Submersible Pump

The submersible pump is the safest method because it does not rely on the pool's primary filtration system, which can be damaged if it runs dry.

1. Connect the discharge hose to the pump outlet and secure it with a stainless steel hose clamp.
2. Lower the pump into the deepest part of the pool. Use a nylon rope attached to the pump handle to lower it rather than the power cord to prevent internal wiring damage.
3. Run the discharge hose to the pre-identified drainage point. Ensure the hose is laid flat without kinks or sharp bends that could create backpressure.
4. Plug the pump into a GFCI-protected outlet.

Pro-Tip: Place the pump on a small plastic crate or a heavy-duty bucket lid if there is significant debris on the pool floor. This prevents the intake from sucking up leaves or silt that could overheat the motor.

Step 3: Configuring the Main Pool Pump (Alternative Method)

If you do not have a submersible pump, you can use your pool’s circulation pump, provided your system has a multiport valve.

1. Turn off the pool pump at the breaker.
2. Close the skimmer valves and ensure the "Main Drain" valve is 100% open. This ensures the pump draws water from the bottom of the pool.
3. Rotate the multiport valve handle to the "Waste" position. This bypasses the filter media and sends water directly out the backwash line.
4. Switch the pump on and monitor the water level closely.

Warning: Never use the "Backwash" setting for a full drain. This can damage the internal lateral pipes in a sand filter or the grids in a DE filter due to the prolonged high-velocity flow.

Step 4: Monitoring Hydrostatic Pressure and Shell Integrity

As the water level drops, the weight of the water—which provides counter-pressure against the surrounding soil—is removed.

1. Locate the hydrostatic relief valves on the pool floor. These look like small plastic caps.
2. As soon as the water level is low enough to reach them safely, use a wrench to remove the plugs. This allows groundwater to enter the pool rather than pushing the pool out of the ground.
3. Observe the plaster or vinyl liner. If you see signs of "bubbling" behind a liner or cracks appearing in plaster, stop draining and refill immediately.

Step 5: Managing the Final Inches and Cleanup

Pumps generally lose prime or suction when the water level reaches about one to two inches.

1. For submersible pumps, stay near the pump as the water clears. Once it begins sucking air (audible as a slurping sound), unplug it immediately to avoid thermal overload.
2. Use a wet/dry shop vacuum to remove the remaining puddles around the main drain and the hydrostatic valves.
3. Inspect the pool surfaces for stains or scaling while the shell is empty. This is the optimal time for an acid wash or tile cleaning.

Technical Specifications and Pump Performance Comparison

Choosing the right equipment determines whether your project takes six hours or twenty-four. Use the following table to calibrate your expectations and equipment selection.

Common Failure Scenarios and Field Fixes

Even with professional-grade equipment, site-specific variables can disrupt the drainage process.

Scenario 1: Pump Running but Water Flow is Negligible

• Root Cause: The pump is experiencing "air lock," where a bubble of air is trapped in the impeller housing, preventing suction.
• Actionable Fix: Tilt the submersible pump at a 45-degree angle while submerged to allow the air bubble to escape through the intake. For a main pool pump, turn off the system, reopen the pump lid, fill the basket with water to the brim, and reseal before restarting.

Scenario 2: The Pump Shuts Off Repeatedly

• Root Cause: Thermal overload protection is tripping because the motor is overheating, likely due to a restricted discharge hose or a clogged intake screen.
• Actionable Fix: Inspect the discharge hose for kinks. Remove the pump from the water and clear any hair, leaves, or calcium flakes from the intake screen. Ensure the extension cord is at least 14-gauge; undersized cords cause voltage drops that lead to overheating.

Scenario 3: Water is Backing Up in the Clean-Out Port

• Root Cause: The flow rate of the pump exceeds the drainage capacity of the home’s sanitary sewer line.
• Actionable Fix: Install a ball valve on the discharge hose to manually throttle back the flow rate. Alternatively, use a smaller diameter hose to increase friction and naturally slow the GPM to a level the sewer line can handle.

Frequently Asked Questions

How often should I perform a full drain of my swimming pool?

In most climates, a full drain is only necessary every 3 to 5 years. This interval is dictated by the accumulation of Total Dissolved Solids and stabilizer levels that make water chemistry difficult to balance. Pools in areas with high evaporation rates or hard water may require more frequent partial drains to manage calcium levels.

Can I leave my pool empty for several days while I clean it?

No, it is highly discouraged to leave a pool empty for more than 24 hours. Prolonged exposure to UV rays can shrink and crack plaster or cause vinyl liners to become brittle and lose their shape. Furthermore, an empty pool is susceptible to structural failure from hydrostatic pressure if the ground becomes saturated by unexpected rain.

Will draining the pool with the main pump damage my filter?

Draining using the "Waste" setting on a multiport valve will not damage the filter media, as the water bypasses the sand or DE entirely. However, if your system uses a cartridge filter and does not have a three-way valve before the filter tank, you risk clogging the expensive cartridge elements with concentrated floor debris.

What is the safest temperature to drain a pool?

The ideal temperature range is between 50°F and 80°F (10°C to 27°C). Draining in freezing temperatures can lead to ice formation in the plumbing, while draining in extreme heat can cause the plaster to dry out too quickly, leading to "crazing" or spider-web cracking on the surface.

How do I know if my pool has a hydrostatic relief valve?

Most in-ground concrete and gunite pools have these valves located in the floor, often integrated into the main drain pot or scattered across the floor in 2-inch diameter white plastic fittings. If you are unsure, consult your original pool blueprints or a local pool professional, as failing to open these during a drain in high-water-table areas can be catastrophic.

Professional Maintenance and Support

Once your pool is drained and cleaned, ensure you follow a structured refill and chemical startup sequence to protect your investment. For advanced structural repairs or complex plumbing configurations, consult with a certified pool technician to ensure your facility remains compliant with PHTA standards.