The simple solution is stitch a fold of nylon grossgrain ribbon or a strip of folded nylon fabric in the center of a 6" disk of compatible fabric. If the tarp is silnylon, use sylnylon of the same weight. You can glue the silnylon disk directly to the tarp and forget about stitching. Squeegee a very thin layer of 100% clear silicone sealant on both the tarp and the patch, put them together, squeegee the bubbles out and put a heavy book on top for 24 hours.
It you insist on stitching, you don't have to hem silnylon, just zigsag around the edge - after the sealant sets. Then seal again on the outside. Glueing first replaces pinning and ensures a neat, waterproof job.
Ray Jardine's directions for side pull outs is to stitch a disk wherever you want it and cut 2 parallel slits in it about 1 inch apart. The piece between the slits becomes the pull-out. It can't get any simpler than that, and, surprisingly, it works. I don't like the fact that water collects between the patch and the tarp. But that's the only down side I know of. It is the lightest pullout.