No prewashing is required but if you are going prewash your fabric, do so for the test also. It does not matter what kind of container you use for soaking. Fabrics can be cut to printer size first or cut afterwards. Air dry fabric. Some report success with letting it hang to dry, others report that they keep it flat on a towel to dry .
Manufacturer states that a blow dryer maybe be used to dry the soaked fabric.
Iron your fabric smooth with regular fabric setting for fabric type, then apply to freezer paper for stability to run through printer. Iron the shiny side of the freezer paper to the wrong side of the fabric. Cut fabric to paper size accepted by printer. If you have multiple settings for ink, the product developer has suggested the highest quality will give the greatest penetration of fabric fibers. I would also suggest that you experiment with Ink Settings to determine the best printout from your printer.