What is this?
We built a new house, moved in about 2.5 yrs ago. I have rust stains in the toilets, so figured it was iron in our water that kept making a stain dripping from tub overflow. Finally removed the plate to clean under, since I started noticing rust "scale" under edge of the cover. WHAT is this (steel?) plate on the bottom edge of the hole for? Looks like there is a black rubber seal on the bottom edge under it, b/t it and the pipe, though not b/t it and the acrylic tub. It's screwed into the pipe, can I remove this and just screw the cover directly into the pipe? Do I need to put a gasket under the cover? We have iron in the water, but I believe most of the problem here is due to this plate corroding (and black gunk collecting under as well as rust - yuck!). Thanks.