You didn’t specify what material the tub was made of, or why an overlay interferes
with the drain. The usual drain removal tool is a tub drain wrench. If the tub drain has no crossbars or the
crossbars have been stripped, try a tub drain key (specialty plumbing tool which wedges against the interior diameter of the drain). Failing that, it’s a precision hacksaw like Tiny Tim
(ugh!).
I assumed
you want to remove the drain itself, not the drain cover, which is simply screwed into the drain and (usually) easily removed with a screwdriver. If the drain cover has been caulked, cemented or otherwise partly covered over, that’s a problem. I don’t know
what the covering material is, but you might be able to clear it away with a
carborundum grinding disk or cylinder driven with a power tool like a Dremel.
That’s going to be precision work, and likely leave some marks. I had to do something like that to grind off ceramic tile around an HVAC vent that
the tilers intruded upon.
-Stuart
.
