Jen- if you have the sanding sponges, they are my favorite thing to use for the back of clay. I lay them on a flat surface- I just cut small pieces out of the big squares and line them up going from fine through microfine grit. Figure 8 as Kathy said. After firing I do tumble but find that using my burnisher on the backs cuts down on PMC porosity- and I mean burnish- don't be whimpy. If it's too tiny, just plan on using more solder than you think you will need. I'd try a few test pieces that you don't think turned out as well as you like first. Any flange I just use needle files and then clean them with your file card after because the dust really sticks in those. PMC is wonderful but it does have it's idiosyncrasies