Most inground vinyl lined pools should have a pipe that connects the void behind the liner to a drain or some external point which is used during the initial installation of the liner as well as for removing water accumulated behind the liner and other service tasks. This pipe is commonly referred to as a “vacuum pipe” and should be installed so the outlet is at least 450mm (18”) below the normal pool operating water level so it can be self draining. Sometimes due to a level site, there is no option but to have the outlet for the liner “vacuum pipe” below the water level and therefore it may be plumbed to the suction side of the pool pump or to a storm water drain.
If the pipe has been connected to a storm water drain, it should have a non return valve so that in times of heavy rain, the water does no flow back in behind the pool liner. Sometimes these are not installed and other times the non return valve can fail and cause a large amount of water to flow behind the liner and the liner to “float” and become wrinkly and spongy. If you suspect the pipe is connected to storm water, locate the pipe and disconnect it from the storm water pipe to prevent the water flooding in behind the pool liner. Install a non return valve and then reconnect it.
If the pipe has been connected to the pump suction inlet, it would have been installed with a 3-way valve and the valve needs to be opened whilst the pump is running to suck the water from behind the liner. Whilst the water is being sucked from behind the liner, use a pool broom to gently push the liner back into position so there are no permanent wrinkles left behind. If there are wrinkles, they can only be moved by draining the pool down to the level of the wrinkles. This is best done by an experienced liner installer or service person.