mtco wrote:
This is the ASCII-art drawing I said I was going to post. (Previous
attempts using HTML formatting produced garbled messages--reverting to
plain ASCII. View the diagram below in fixed width font.)

------------ --- shower drain strainer
| | --- small tabs bent to point downward
___ ___
'--... ...--'
||| ||| --- Middle ring: black rubber?/plastic? gasket?
| | | | --- Outer ring: PVC shower drain
| |
| | --- Inner ring: PVC drain pipe
| |

Note: tops of drain pipe and gasket? too high, interfering with
the "tabs" on the strainer

I don't see why you need the tabs. According to
your diagram, if the strainer is sized right it
would fit in the depression. You could put a very
thin amount of plumbers putty in the depression
ring and just press the strainer into it. Cut the
tabs off or just bend them flat. Or, get a
strainer that has tabs spaced to fit inside the
drain pipe.