With Tupperware, I like to drill holes so the bedding will have "footing", can't come out. Bedding material sometimes doesn't stick that well to Tupperware.
Synthetic stock molds are often sprayed with a release agent so they'll come out of the mold cleanly. Clean the inletting thoroughly and giving it some tooth by rough sanding, drilling and/or cutting some light grooves helps too.
If you need a quick release agent try Kiwi Neutral Shoe Polish. Cheap and you can buy it just about anywhere.
