I did not pump water out from behind my liner. There was only enough behind it to lift the liner up slightly.

Try to upload photos to photobucket and then link here with the add photo icon.

A brush won't have the same pushing power as your hands or a squeegee. There is a type of rubber squeegee that has curved edges that you can attach to a pole. I also have a rubber pool "brush" that has a squeegie on the opposite end, but those are hard to find.

If the water is just sinking back down the wall when you push it, you might try pulling the coping out a tad and see if you can push the water out?

See if you can load those pics.