It's been about 10 years since we've had to force the PVC liner down into the ground. We filled the liner with water, assembled the casing as we lowered it in. After the casing was in, we pumped out a foot or two of the water. Then we poured a product in to seal the water in. As Magic Smoke said if there is no oxygen, rust will not form. Sorry I can't remember the product name.
