Tub Drain

I just installed a new cast iron tub....I used new PVC parts for the drain connections to the existing pvc trap. I seemed to have a leak where the drain meets the tub drain (the tub shoe). The new drain had a rubber gasket and I used both plunbers putty under the brass drain(in bathtub) and Teflon thread dope. Can you tighten the drain too much?? Any suggestions why this might be leaking....all other connections are pvc compression fittings that are fine.

The rubber gasket is making the seal, the putty is keeping water from getting underneath the upper flange and is mostly cosmetic. You normally would not need the pipe dope - this is used on a tapered pipe thread, the nut holding the gasket is not tapered. there is often a fiber or paper washer between the nut and the rubber gasket. If that is missing, when you tighten the nut, you can cause the rubber gasket to bunch up. The washer spreads the pressure out a little and acts to prevent the bunching of the gasket when you tighten things up. Omitting that washer may be the problem. If the quality is slipping, the area where that rubber gasket goes could be rough or have a crack in it. It would leak from there.

of course there was no washer in the package....I have the old one from the old bathtub.....is it correct that it goes below the rubber gasket??

Tub, gasket, washer, nut...

washer

DO NOT use a paper/fiber washer under the tub. The rubber gasket is under "straight line" compression only so there is not rotary force trying to twist it out of position. It is also too firm to distort that way in any case. The cardboard washer can absorb water then deteriorate which WILL cause a leak. If it leaks under the tub you either do not have it tightened enough or you have an unever bottom on the tub.