i am connecting 4 inch cast iron pipe to 4 inch pvc pipe using a fernco coupler. the coupler is the correct size yet it (the coupler) fits somewhat loosely around the iron pipe (there is about a quarter inch gap between the outer surface of the pipe and inner surface of the fernco). can i use a lap/gutter rubber butyl type caulk and fill in this gap before i tighten down the metal strap on the fernco? i don’t want any water getting in there. maybe this is overdoing it a bit.
If you are using just a regular rubber fernco coupling you are using the wrong fitting….though it can work. What you really need is a 4″ CI 4″ Plastic Proflex coupling by Fernco. This will give not only a better fit, but a stronger/stiffer connection. Proflex coupling
thanks for the information! perhaps you can answer a question: is there a pvc coupler that connects 4″ to 4″ pipe but fits inside the pvc pipe (instead of outside the pipe)? i’d like to have a bit pipe that i can stick inside the existing iron pipe. that way no worries about water ever getting outside the existing drain pipe. i’d still use the fernco.
after busting up a concrete floor i never want to think about this again – whew
You could use a Fernco donut in the hub of the cast iron and connect the PVC that way, but you’d never be able to get a Fernco coupling on the pvc AND the hub of the cast iron. If I had the choice between the two, I’d go with the coupling. I’ve put in more than I can count over the years and have yet to have one fail.