Concrete also sticks very well to plastic. Treating plastic with a release agent prior to coming in contact with concrete is the best way to ensure your plastic buckets and tools remain free of dry concrete.

How do you keep concrete from sticking to plastic?

It's usually a silicone based spray, but there are various types. Liquid sprays that don't dry wouldn't survive the initial pour. Using solid vegetable shortening on the sides should make it stay there, otherwise you could use a liquid or solid wax that dries to a film.

Does concrete stick to PVC pipe?

Mix enough concrete to fill the area you require using water and "hydraulic" cement powder; prepare the mix in a large, plastic container. Hydraulic cement expands as it cures, and will form a tightly packed structure around the PVC pipe.