I did a little plumbing this morning, and took apart some pipes that I
put together several years ago with Master Plumber Yellow #5. The label
says it is non-hardening and prevents thread corrosion. It apparently
really works. The pipes came apart as easy as they went together.
Good stuff. Leak-free joints are easy, and so is changing the plumbing
years later. It's good for both plastic and metal threads.