Step 5 · Install the Compression Gasket
Take the rubber 'donut' gasket and apply a liberal amount of plumber's grease or a thick soap and water solution to its entire outer surface. Also, apply lubricant to the clean inner surface of the cast iron hub. To install, fold the gasket slightly (like a taco) to get it started in the hub opening. Then, using firm and even pressure with your thumbs, press the gasket into the hub until its outer flange sits flush against the face of the hub. Ensure the gasket is not twisted inside the hub.