There are many ways to do it, but with plastic foundation I generally use a cake slicer type spatula to scrape off the cells of honey onto a glass cutting board (you don't want to damage the foundation or scrape off all of the wax coating), then mash up with something like a potato masher, then scrape into a clean home depot paint strainer stretched over a 5 gallon food grade bucket. Let it drain and settle. Squeeze and tighten paint strainer as necessary. Let bees clean up ball of wax.