Can or should you use a suction cup to help pull an in-ground swimming pool liner into place?

During initial installation, it is best to do this with your hands, or even Duct Tape. If using duct tape, be sure not to leave the tape on for long. After filling with water, a suction cup or a good old fashion plunger (new!) work great. I've used a plunger on hundreds of liners. The only chance of damage I've seen is to the sand or still wet vermiculite bottom. For those impossible to move wrinkles, putting a small amount of water behind the liner can make the job much easier. I would recommend a professional for this though.