Putting in a piece of 4 inch schedule 40 between 4 inch cast iron I’m
Using fernco coupling 1056-44. However I’ve found the cast iron is slightly smaller than the schedule 40 and the coupling is a little loose. I’ve torqued the coupling down 60 inch pounds and noticed it is a little crimped. Water from the shower and sink run perfectly and I have flow all the way to the street. But the toilet seems to have a weak flush and is gurgling when flushed. Is there another coupling that would give me a better seal? Some sort of reducer that I could put on cast iron before attaching coupling? Or is this just another issue that may have been caused during the initial back up that may have effected something like the vent pipe?
Forgot to mention the pipe I’m repairing is below ground,



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Nothing wrong with that coupling
It is most likely not causing your toilet problem
You will need a src-19 band to make the coupling legal… especially for underground use
There may be a partial clog in the toilet or the water level in the tanks is too low



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I had a similar experience connecting a 3" new PVC pipe to old 3" CI pipe from the 1950s. There is SV Service Weight cast iron and there is XH eXtra Heavy cast iron with different ODs. In addition, there could be slight variations depending on the foundries. Finally, as I have discovered, some old cast iron pipes were made in copper pipe sizes. What I ran into was the Fernco coupling was too loose on the CI side to the point the metal sleeve crimped badly as I torqued it down.

This is a thread a few years back with discussions of this issue and my eventual solution with pictures. It may or may not be relevant to your particular situation, but if yours is too loose, with careful measurements, Fernco does carry many rubber adapters that fits inside their standard "44" and "33" couplings. Use the strong back sleeves.

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