For getting gooey stuff (like tomato paste or watermelon) off of the plastic liners used with dehydrators, throw the liners into the freezer for a while. The frozen stuff will crack off of the liner with relative ease. Some tough cases (crushed tomatoes) may need several freeze cycles.

One warning  :o, work fast to get the stuff into bags or containers as frost from the air quickly forms on the frozen stuff, partially rehydrating it. This has never been a real problem for me as I usually over dry stuff that would normally be gooey.

-aj