Haven't done this before--
I wonder, is there supposed to be a gasket between the tub shoe and the bottom of the tub? As the picture shows, there is no gasket there visible from under the tub.
Do I drop the gasket in from above after I remove the drain flange, or I need to remove the tub shoe from under and slide it in under the tub and then reinstall the tub shoe?
Also, do I need to ensure where the rubber gasket meets the bottom surface of the tub and the top of the tub shoe are smooth (use sand paper to sand it down if there's rust?)?
And, would I need to apply silicone sealant to the top/bottom of the rubber gasket?