Replacing top half of solvent weld shower drain
A little advice here would be most appreciated...
Six year old home, slab on grade, one-piece fiberglass shower unit with solvent weld drain over what looks to be a 2" PVC pipe. Original installers must have overtightened the screws that hold the strainer down. In doing so they broke the molded-in plastic "nuts" underneath. This was not realized until I removed the strainer to clean hair, etc. from drain. So now I must replace the top half of the drain to make it right. Why it hasn't come loose sooner is beyond me.
I think I understand how this would have originally been installed. You would, of course, have access to the underside of the fiberglass unit. The drain, I gather, would have been attached to the shower with caulk or putty placed under the top lip, tightened from the bottom squeezing the O-ring and fiber washer, and the whole deal very carefully placed over the drain pipe covered with solvent cement. Glad that wasn't my job! Seems like there would be an easier way.
Anyhow, I have similar drains from two different manufacturers for replacement. The local plumbing supply house just said, "... unscrew the top of the old one and screw the new one in... " Sounds easy enough, but the one that's in there obviously didn't have one of those fancy "locking wrenches" as Oatey calls it because there are no grooves for it. I only know this because one of the potential replacements came with such a thing and it looks like it would be very handy. So first question... is the old channel locks and screwdriver trick the best way to get the old one out? Secondly and assuming that one of my potential replacements matches the existing threads, is it as simple as applying silicone to the underside of the lip and screwing in (i.e. should I worry about putting too much torque on the glue joint(s) below)? And third, if the replacement without the locking wrench has the matching threads what's the best way to tighten it down (channel locks and screwdriver again)??
Thanks for the help!