Fiberglass pool sump tubes and why they are important
An ounce of prevention is worth a pound of cure. In the pool industry this saying most certainly applies to the use of use and installation of sump tubes. Sump tubes are pipes installed at the deep end of a pool that run vertically from the pool deck to the very bottom of the pool floor. Diameters may vary, but it must to be large enough to allow for a sump pump to be placed into the well – typically 8".
In order to understand why a sump tube is important you must first understand what forces are at work. Each area of the country have different ground water levels. When an in ground pool is installed typically there will be a time when ground water is at a level higher than the bottom of the pool. In the industry we refer to this as "water underneath" or "around" the pool. As the ground water rises, the pool (or vessel) becomes buoyant. In the case of a boat buoyancy is good. For a pool not so much. By installing a sump tube the installer and owner have a measurement of how much water is under the pool and more importantly have a way of pumping it out.
Typically water under the pool is normal and not a problem. However when your pool is first being installed, there is always a chance that before the concrete is installed and holding the pool in place, a heavy rain could occur and increase the chances of the pool shifting. This is why until the deck is completed, a sump pump should be dropped into the sump well to keep the ground water out of the hole. Once the pool has concrete poured around it the ground water level can safely rise to within 16" of the pool water level.
Outside the initial construction of the pool the sump tube will continue to be cheap insurance. It offers the owner and service people the ability to know what the ground water is doing should the pool need to be drained or there be a period of heavy rain in where the ground water might exceed the level of the pool water. All pool types are subject to the laws of physics. If you are considering having an in ground pool installed, demand your builder install a sump tube, and hopefully you'll never need it.