A few options (not exhaustive):
- It will probably work just by cranking down on the hose clamp, although I'm not a huge fan of that idea.
-What type of SDR35 pipe are you using? If solvent weld, gluing a hub from a piece of hub-end pipe onto the SDR35 will increase the OD, and it will probably end up very close to what the Fernco is intended for.
-Or they make thin solvent-weld bushings for this purpose, e.g. (random example):
PVC Adapter reducer bushing 6" solvent glue
drainageproducts.us
-Never tried Fernco's HULK fittings, but the HULK5 says it will work for ODs from 5.30" to 6.7", so that should cover 6" SDR35 at about 6.3".
THE HULK COUPLING Universal Sewer and Drain Repair Coupling.
www.fernco.com
Cheers ,Wayne