We have a cast iron pipe leave the house with PVC connected to it at the wall with a "donut" style adapter like this:

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Basically you stick the donut into the cast iron pipe and PVC into the donut and it forms a watertight seal.

I haven't been able to find out what length of PVC is meant to enter the donut. Ideally I'd like to use a 90 elbow with a spigot end - (meaning one end is the same diameter as a pipe) but on a 3" PVC pipe that end only has a 1-1/2" long section, which I think would be too short.


The piece of PVC should be long enough to extend to the end of the donut when it's inserted into the pipe. The seal is increasingly improved the further the PVC is inserted so you don't want to cut it short.

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