To put a liner on an above ground pool with a shop vac, follow the steps below:
Drain your above ground swimming pool by opening the main drain plug or by using a pump.
Remove the old liner using a sharp utility knife.
Fix and level the cove, walls, and padding or floor. Remove any debris that can puncture or damage the underside of the pool liner.
Bring the pool liner into the middle of the pool. Carefully stretch the pool liner outwards or towards the walls, smoothing out large wrinkles as you go along.
When the edges have reached the pool walls, pull the walls of the liner above and over the pool walls. Attach the pool liner using pool copings.
Insert the from the shop vac through the return hole on the pool wall. Angle the hose downward so that it sucks the air from the bottom first.
Fill the pool liner with several inches of water and smooth out any wrinkles in the liner.
Turn on the shop vac to remove the air between the pool liner and the pool floors and walls. Once the liner has attached itself to the pool structure, you can turn off the shop vac and proceed to fill the pool with water.