Maintaining a swimming pool requires attention to every component of the system, including the main drain. Whether you’re winterizing your pool, performing repairs, or temporarily shutting it down, knowing how to plug a pool main drain correctly is crucial. A properly plugged main drain can prevent water loss, inhibit debris from entering your pool lines, and protect the equipment from unnecessary wear and tear.
This step-by-step guide will walk you through everything you need to know about safely and effectively plugging a pool main drain. From understanding your system’s layout to selecting the right materials and best practices, we’ve got you covered.
Understanding the Role of the Pool Main Drain
Before jumping into plugging the drain, it’s important to understand what the main drain does and when it should be closed or plugged.
What Is a Pool Main Drain?
A pool main drain is typically located in the deepest part of the pool, either at the bottom or on the slope of the deep end. Its primary job is to draw water from the pool and send it toward the pump and filtration system. While the skimmer handles surface debris, the main drain ensures even water circulation throughout the pool.
Why Would You Plug the Main Drain?
There are several reasons why you might want to plug the main drain:
- Winterizing the pool – To prevent water from freezing in the lines and causing cracks.
- Performing repairs – Like replacing a pump or filter, or repairing leaks in the plumbing lines.
- Maintenance tasks – When draining the pool or servicing the plumbing system.
Types of Main Drains and Plugging Methods
Depending on the age and type of your pool, you may have different styles of main drains that require slightly different approaches.
Screw-in Main Drain Covers
These are the most common drain types in modern pools. They have a threaded drain outlet and are usually covered with a grate or a plastic or stainless-steel drain cover. Plugging this type is relatively straightforward — you can usually screw a pool plug or cap into the existing thread.
Drains with Flanged Covers
Older pools might use flanged drain covers that are bolted to the pool floor. These require a more involved process to remove, plug, and reseal since you’ll need to deal with bolts and possible sealants.
Automatic Drains and Check Valves
Some pools use automatic drains that are equipped with check valves to prevent water from flowing backward into the pool or the plumbing lines. These systems may not need manual plugging as part of winterizing, but knowing how to bypass or isolate them properly is still important.
Tools and Materials Needed to Plug a Pool Main Drain
Before you begin the process, gather all necessary tools and materials to avoid interruptions during work. Having the right supplies ensures efficiency, safety, and proper water protection.
| Tool/Material | Use |
|---|---|
| Screw-in Pool Drain Plug | Covers and seals the drain outlet, preventing water and air pressure issues. |
| Teflon Tape or Thread Sealant | Ensures a tight seal on threaded plugs to prevent leaks. |
| Rubber Gasket (if applicable) | Used with flanged drains for added sealing protection. |
| Socket Wrench or Screwdriver | Used to remove existing drain cover bolts. |
| Silicone Sealant (for flanged systems) | Provides a waterproof bond between drain plate and the pool surface. |
| PVC Pipe Plug (if plumbing is accessible) | Useful if you’re isolating water at the line rather than directly at the drain. |
Step-by-Step Guide to Plugging the Main Drain
Now that you understand the system and have your tools ready, let’s dive into the actual plugging process. This method works best for modern, screw-in style main drains, but we’ll also cover additional considerations for flanged or older-style drains.
Step 1: Drain or Reduce Pool Water Level
Caution: Never try to plug a submerged or fully underwater main drain without de-watering—this is extremely dangerous and can damage the system. If you’re preparing for winter or major repairs, drain the water down just below the skimmer or completely empty the pool if local regulations allow.
- Use a submersible pool pump or have a professional drain services complete this step.
- Ensure the main pool pump is turned off before beginning.
Step 2: Remove the Drain Cover
Using a screwdriver or socket wrench, carefully remove the screws or bolts holding the drain cover in place. Keep all hardware together in case you need to reattach the cover later.
- Set the cover aside in a safe place.
- Inspect the drain outlet for debris, algae, or buildup.
Step 3: Clean the Drain Outlet
Use a rag and mild cleaner or disinfectant to wipe the threads or edges of the drain outlet. Keeping the area clean will help prevent air leaks and ensure a solid plugging seal when using screw-in or threaded components.
- Avoid using harsh chemicals that may wear down plastic or rubber seals.
- Make sure the drain has no cracks or unusual wear before sealing.
Step 4: Apply Teflon Tape or Sealant
If you’re using a screw-in drain plug, apply a thin layer of Teflon tape around the threads. This helps create a secure, watertight seal. This is crucial to avoid pressure imbalance that could damage the plug or lead to water leakage.
- Wrap the tape 3 to 5 times in a clockwise direction, matching the threading direction.
- Ensure even coverage without over-wrapping.
Step 5: Insert and Tighten the Plug
Carefully screw the plug into the main drain using hand pressure first. Once it’s set, use a wrench or hand tool to tighten it securely.
- Tighten until snug; over-tightening can damage threads or break the plug.
- Check for leaks by visually inspecting or using soapy water. If bubbles appear, reseal properly.
Step 6: Reinstall Drain Cover (Optional)
If the original drain cover is in good condition and your local codes don’t prohibit its use after plugging, you may reattach it using the original bolts and gaskets. This helps protect the plug from shifting or becoming dislodged, especially during pool winterization.
- Apply a dab of silicone sealant to bolt holes for extra security (particularly with flanged covers).
- Keep access points marked if professional maintenance might be needed later.
Special Considerations When Plugging Older or Flanged Drains
Plugging an older-style main drain that uses a flanged cover involves a bit more work, but the procedure follows similar safety and sealing principles.
Removing the Flanged Cover
Flanged drain covers are bolted directly to the pool floor using 4 or more bolts secured around the edge. Removing them requires patience and a properly sized wrench or ratchet.
- Be cautious of rusted bolts — apply a lubricant like WD-40 to ease removal.
- If the cover is stuck due to years of mineral buildup, gently wiggle the cover after loosening until it comes off.
Installing a Seal Washer or Gasket
Once the cover is removed, inspect for a gasket. If none exists, or it’s damaged, install a new rubber washer to act as a seal when reattaching.
- Place a new gasket or seal washer over the flange.
- Use stainless steel bolts to prevent corrosion (especially if reinstalling the cover later).
Using a PVC Cap for the Drain Line
If the actual drain pipe is exposed (say, the drain is disconnected entirely), consider capping the exposed end with a PVC pipe plug. This provides additional protection against water and air pressure in the lines.
- Measure pipe diameter accurately and purchase the correct slip-fit PVC plug.
- Apply PVC cement for a permanent seal or use removable plugs if future use is anticipated.
Additional Safety and Best Practices
To avoid accidents and ensure lasting effectiveness of your main drain plug, keep these best practices in mind.
Do Not Use Improvised Covers or Plugs
Using rubber stoppers, tape, or homemade plugs can lead to pressure imbalances, leaks, and potential bursting of pipes — especially during winterization when freezing occurs.
Double-Check Local Codes and Contractor Advice
Some local pool regulations outline the requirements for winterization, including how to safely plug drains. Ensure your method is acceptable and follow seasonal guidelines regarding line coverage and antifreeze use.
Label Plugged Areas for Professionals
If you’re working on parts of the plumbing and not the drain directly, but have altered the system, mark all modifications for future service teams.
Plug the Skimmer Too
Whenever you’re plugging the main drain, also ensure the skimmer lines are plugged or fitted with an in-line freeze guard to prevent the entire system from freezing.
Consider Professional Help for Complex Systems
If your pool has older plumbing, a complex filtration system, or combined return lines, hiring a professional may be the safest and most cost-effective option.
Common Mistakes to Avoid
Avoiding errors during the plugging process is crucial to prevent costly repairs or damage. Let’s take a look at common missteps and how to sidestep them.
Over-tightening the Drain Plug
Although you want a secure fit, over-tightening a threaded plug can strip pool drain threads, especially in plastic components. Always hand-tighten first, then give the tool a final quarter-turn if necessary.
Using the Wrong Type of Plug
The threading type (male/female), thread pattern (NPT), and diameter must all match the drain opening. Using mismatched plugs risks leaks and structural damage over time.
Ignoring Water Flow Issues
If your pool has multiple drains or return lines, always ensure you’re maintaining a balanced system. Plugging only one drain — if others are still open — can cause pressure imbalances or impede proper pumping.
Not Checking for Leaks
After installation, check for leaks using a visual inspection for moisture or air bubbles under water. If bubbles appear around the plug, disassemble and reapply new Teflon tape.
Pulling It All Together: Best Practices Summary
To recap, here’s a quick list of best practices for plugging a main pool drain effectively:
- Always turn off the pump and power system before starting work.
- Drain the pool or lower the water below the main drain level before plugging to avoid water pressure.
- Select the correct plug type and size based on your drain’s threading and configuration.
- Use Teflon tape or a high-quality sealant for a watertight connection.
- Ensure all connections are secure but not overtightened to prevent damage to the drain structure.
- Always plug the skimmer as well if winterizing or isolating the entire system.
- Label or document all plugging modifications for future reference or professional access.
Conclusion: Taking Care of Your Pool Components
Knowing how to plug a pool main drain is not only useful in emergencies — it’s a critical skill for safe seasonal care and efficient repairs. Whether you’re preparing your pool for an off-season, undergoing a plumbing upgrade, or tackling maintenance with a DIY mindset, a well-sealed main drain can prevent expensive damages, prolong equipment life, and enhance water flow stability.
By following this guide and adhering to local codes and system-specific considerations, you’ll ensure your pool is ready for whatever maintenance phase it’s entering. A little time and attention to detail can go a long way in maintaining a clean, functioning pool system.
And if you’re ever unsure or working with an unfamiliar pool setup, don’t hesitate to contact a licensed pool professional to ensure safety and precision.
Why would someone need to plug a pool main drain?
There are several reasons why you might need to plug a pool main drain. One of the most common is during pool closing for the winter season, especially in regions where freezing temperatures can cause damage to plumbing lines. By plugging the drain, you help prevent water from freezing and expanding inside the pipes, which can result in costly cracks or leaks. Additionally, during certain maintenance or repair tasks, such as tile replacement or hydrostatic pressure issues, temporarily sealing the main drain may be necessary to prevent water loss or structural concerns.
Another scenario involves pools that are undergoing seasonal or long-term inactivity. In these cases, draining the pool completely might not be advisable or safe, so plugging the drain offers a secure way to retain water. This also helps maintain the structural integrity of the pool, reducing the risk of it popping out of the ground due to rising groundwater levels. Whatever the reason, choosing the right type of plug and properly installing it is crucial to ensure the drain remains sealed and problem-free throughout the period of inactivity.
What materials are needed to plug a pool main drain?
To effectively plug a pool main drain, you’ll need a few key materials. First, you’ll need a main drain plug, which is typically made of threaded brass or plastic and designed to fit the specific size of your drain. You’ll also require a rubber washer to create a watertight seal, silicone or Teflon tape for added leak prevention, and a wrench or socket set to tighten the plug securely. If you’re using an expanding plug instead, make sure it’s the correct size and type for your plumbing system.
Additional tools may include a wet/dry vacuum to remove residual water from the drain line, a screwdriver if any access covers need to be removed, and a bucket or towel to manage any water that might spill during installation. Safety gear, such as gloves and eye protection, is also recommended to guard against potential slips or chemical exposure if you’re working around pool chemicals. Ensuring you have all the necessary materials and tools before beginning will make the plugging process more efficient and reduce the risk of leaks or improper installation.
Can I use a regular plug for my pool’s main drain?
Using a regular hardware store plug is not recommended for a pool’s main drain. Pool main drains are typically designed to handle higher water pressures and must form a secure, watertight seal to prevent leaks and structural issues. Standard plugs may be made of unsuitable materials, may not fit properly, or may degrade when exposed to pool water chemicals or underground moisture. Specialized pool drain plugs are specifically engineered for these applications, offering durability and a secure fit that helps protect your pool and plumbing system.
Instead, it’s best to purchase a drain plug designed for in-ground pools. These usually come in threaded brass or expanding rubber styles that are compatible with standard plumbing setups. Threaded plugs can be screwed into place with a washer for a leak-proof seal, while expanding plugs are inserted and then tightened to create a secure fit. These specialized options are widely available at pool supply stores and are well worth the investment to avoid costly damage later.
How often should I check the main drain plug after installation?
After installing a plug in your pool’s main drain, regular inspections are important to ensure it remains secure and leak-free. It’s advisable to check the plug at least once a month during periods of pool inactivity, such as the winter months. Even small leaks can lead to significant issues over time, potentially causing flooding, plumbing damage, or disruptions to the pool structure. Regular inspections can help catch problems early and prevent costly repairs down the road.
During each check, look for signs of moisture, pressure changes, or displacement around the plug. If your pool has a hydrostatic valve, also inspect that component, as it may be affected by changes in groundwater levels. If you notice any water seepage or movement in the plug, remove and re-install it with a new washer and sealant if necessary. Staying proactive with simple maintenance tasks like this can help protect your pool during off-seasons and extend the life of your equipment.
What is the best way to remove a plugged main drain?
Removing a plugged pool main drain should be done carefully to avoid damaging the pool plumbing or surrounding area. If you installed a threaded plug, use a wrench or socket set to carefully loosen it in a counterclockwise direction. Applying a little penetrating oil can help if the plug is stuck due to mineral buildup or corrosion. If you used an expanding plug, simply loosen the center bolt to release the pressure, allowing the plug to be removed easily. Always be prepared for some water drainage, so have a wet/dry vacuum or pump ready to manage any outflow.
Once the plug is removed, inspect the drain and surrounding area for debris or wear. Make sure there are no cracks or leaks in the pipe before reconnecting the system. If winterization was the reason for plugging the drain, you’ll also need to reconnect any pipes, reinstall fittings, and restore circulation to the pool. Thoroughly flush the lines and ensure all valves are set correctly before starting the pump again. Taking the time to properly remove and inspect the drain will help ensure your pool starts up smoothly and safely for the season.
Are there different types of pool main drain plugs?
Yes, there are several types of pool main drain plugs available, each designed for specific installation needs. The two most common types are threaded drain plugs and expanding rubber plugs. Threaded plugs are usually made of brass or durable plastic and are screwed directly into the drain line, often with a rubber washer to ensure a tight seal. These are ideal for permanent or semi-permanent installations and are commonly used during winterization or long-term pool closures.
Expanding plugs, on the other hand, are typically made of rubber or thermoplastic and are inserted into the pipe and then expanded using a screw mechanism. These plugs are excellent for temporary use and are often a go-to option for shorter maintenance periods or seasonal use when the plug may need to be removed sooner. Each type has its advantages and choosing the correct one depends on the duration of the closure, pipe size, and your comfort level with installation tools. Consulting a pool professional or supplier can help you select the best plug for your specific situation.
Is it necessary to hire a professional to plug a pool main drain?
In most cases, plugging a pool main drain is a manageable DIY task, but there are situations where hiring a professional is the better choice. If you’re unfamiliar with pool plumbing, don’t have the right tools, or are unsure about how water pressure or groundwater levels might affect your pool, it’s wise to seek professional help. A licensed pool technician can ensure your drain is properly plugged, reducing the risk of leaks, pipe damage, or structural issues during periods of inactivity.
Additionally, if your pool has an older or non-standard plumbing system, a professional can provide the expertise needed to address potential complications. They can also offer guidance on whether plugging the main drain is even required based on your climate, pool type, and other system components like a hydrostatic valve. For seasonal maintenance, hiring a professional may also provide peace of mind knowing that winterization was done correctly and your pool is well-prepared for long-term protection.