Swimming Pool Blog

Correcting Hazardous Single Main Drains

Installing Dual Main Drains in an Inground Pool
by Rob Cox  February 20, 2013

Correcting a Pool Main Drain Hazard

Main drain entrapment, or being suctioned down to the main drain of a pool or spa, has had fatal consequences for dozens of swimmers.

The problem occurs when suction is so great through a single main drain, that a person can be stuck in or on the drain, and be unable to escape.

Recently, with the passage of the Virginia Graeme Baker Act (VGB), public pools and spas are required to install dual main drains with anti-vortex main drain covers.

Residential pools are not required to retrofit their pool for dual drains, but most pool builders are now installing two main drains instead of one. Service companies and pool owners should check for non-compliant main drain covers. Generally speaking, flat grates encourage entrapment, while domed covers, with holes on the side of the main drain cover, do not. Almost as important, however - is that drain covers are properly secured, with both screws.

Many residential swimming pools have main drains that are connected into the skimmer, with one pipe running to the pool pump. In these cases, entrapment is more difficult, as the suction from the drain is offset by the suction from the skimmer. That is, if the main drain were to be blocked (by a person) the suction should shift to the skimmer - in theory anyway.

For residential pools that have a dedicated main drain line - running all the way back to the pump, a hazard exists. If the skimmer valves were closed, and all of the pump suction is from the main drain only, a swimmer could become trapped on the main drain - in a pool or spa.

There are 3 methods of correcting a hazardous situation from a dedicated main drain line.

Abandon the Main Drain line

In some older pools, it's not uncommon to find the main drain line has leaked or collapsed and been sealed up in the main drain pot, and the piping removed from the suction side of the pump. The APSP has produced a case study on pools without main drains, and the CPSC has this to say about it.

"CPSC staff recommends that to ELIMINATE and not just MITIGATE the drain entrapment hazard in pools and spas, pool owners should disable old drains or build new pools without any drains and use gutters, overflows and/or skimmers to provide water to the pump."

If your pool is shallow depth, not having a main drain will have less of an effect on water quality. To compensate for the lack of a main drain, return jets can direct filtered water to the deep end of the pool. Automatic pool cleaners can also take up the slack, helping to distribute filtered water and improve circulation.

To abandon the main drain line, you can fill in the main drain pot with concrete, but you don't have to. It may be a good idea to plug the line to prevent future leaks. On the other end of the main drain pipe, in front of the pump, cut and cap the pipe.

Install a Vacuum Release System

A Vacuum Release System, or VRS, senses the vacuum pressure that is before the pool pump. When a drain is blocked, fully or partially, this will raise the vacuum pressure on the main drain line quickly and immensely. The VRS senses the pressure change and shuts off the pump.

Vacuum Release Systems have saved countless lives, and are required equipment for many commercial pools. Installation takes about an hour, and in many cases, installing a VRS is the most cost effective solution to a hazardous main drain. Correctly installed and compliant main drain covers should also be used.

Install Dual Main Drains

This may seem like the most work, but it is what most commercial pools with single main drains are required to do, to bring their pools into compliance. Adding a second main drain to your residential pool can be done for plaster or vinyl liner pools, and the steps would look like this.

  • Drain Pool completely, open up any hydrostatic relief valves.
  • Using a large Chop Saw, cut open a channel in the pool floor.
  • Using a small Jackhammer, break up the gunite and plaster.
  • Cut the pipe that enters the main drain and install a Tee fitting.
  • Connect two main drains, 3-4 feet apart, to the Tee fitting.
  • Fill the hole back in with hydraulic cement, cover with plaster.

For vinyl liner pools, the process is similar, with the exception of pulling back the liner first, to access the floor. The liner will also need to be replaced, now that the hole for the single main drain will no longer line up.

Residential pools are not required to do anything at this point, but if you are worried about entrapment in your pool or spa, it would be wise to take one of the listed steps to correct the situation.


If you do nothing, at least do this - make sure that your main drain covers are secured tightly - limb entrapments also occur, not from the suction, but from getting toes or hands caught in a main drain. If you main drains have flat grates, you should also install anti-vortex main drain covers.

This is important for pools, but perhaps more important for the pool/spa combo. Inground spas often do not have a skimmer, but isolate ALL of the suction through the main drain only. If incorrect or loose fitting spa drain covers are in place, a tragedy could occur.

If you have a pool and spa combo, and only a single drain in the spa (some have drains also on the side), you may have an even more hazardous situation, as swimmers are much closer to the drain. Exactly how the world lost Virginia Graeme Baker, in a spa with a single drain.