I pour the batter directly into the PVC pipe. When I begun with PVC pipes I did the extra work of lining it. It is not worth it in my opinion.
For easy unmolding, put the whole pipe into the freezer a few hours so it gets frozen. When you take it from the freezer, let hot water a very short time flow over the pipe and then press out the soap.
Try greasing the mold with lanolin, mineral oil or petroleum jelly. Basically with oils that don't saponify. The best for me was greasing the mold with a decent amount of petroleum jelly before pouring. then there is a dilemma of to use or not to use mineral oil or petroleum jelly at all. eventually i gave up the whole thing and went with silicone moulds.