From http://www.swimmingpoolsteve.com/pages/drain.html - Learn about the dangers of draining your own concrete pool, what hydrostatic pressure is and why it is an important factor for draining concrete pools. This is not a task for the do-it-yourself type; this should be left to the concrete pool professionals. ... https://www.youtube.com/watch?v=A4aguy4ltpw

From https://www.swimmingpoolsteve.com/pages/common-fittings.html - When it comes to swimming pool installations the correct product to use is a pressure rated (schedule 40) PVC pipe. However these fittings are somewhat uncommon, especially if you are shopping from a local hardware store versus a dedicated pool and spa supplier. While the fittings themselves can look very similar, including non pressure rated PVC coming in white also, there is a distinct difference between pressure rated fittings and DWV fittings. DWV stands for drainage, waste and vent and these are not suitable for any pressure application, including pools. Unfortunately most people can not tell the difference between pressure rated PVC and drainage PVC. In this video you will see that the slip joint on the pressure rated fittings is longer than the slip joint on the DWV fittings. This is a dead giveaway for spotting pressure rated PVC fittings. If you have any drainage fittings in your pool system you should replace these with pressure rated fittings. The confusion comes from some suppliers now making pressure rated fittings which also can be used for DWV. So you can have a pressure rated fitting but it also says DWV embossed right in the plastic so it can be confusing whether it is the right thing to use or not. In this case, look at the length of the glue slip joint as illustrated in this video. A pressure rated glue slip joint should be about 1.5" long versus a drainage rated fitting which has a glue slip joint about 3/4" long. #swimmingpoolsteve #poolplumbing #PVC ... https://www.youtube.com/watch?v=tKI76j5xcH0