I am attempting to mate 3" PVC to an existing 4" cast iron tee that is coming off the main vent/stack for the house. I remove a damaged piece of cast iron that from tee as well as the okum and lead. I am left with a 5 1/8-1/4" ID on the tee, it's a bell end, the OD on 4" PVC is only 4 1/2". Should I fill this space with Okum and pipe seal? What would be the best way to seal the PVC to the cast iron? I'm wary about using a Fernco coupling because the OD on the cast is 6 1/4" for about 1" and then tapers down to 5 3/4" for 2" before tapering to 5" where it meets the stack. Should I be using a donut that goes inside the Cast iron? I need help.

-Isaiah

If this were my call I'd repack the oakum and use a lead substitute (see image) and use caulking irons, (see image) to caulk the joint. The reason I didn't suggest a donut is because you need room to lever the PVC in and the room is not always there. You may rent a set of inside and outside caulking irons at your local Rent All. Good luck, Tom

So to clarify, The Red material in the picture is the Oakum and the grey material is the lead substitute? I have a product I found at Lowe's that is made by "Oatey" called "Pipe Seal" with the description "Seals soil pipes and joints". However, on the

isaiahmadden : So to clarify, The Red material in the picture is the Oakum and the grey material is the lead substitute? I have a product I found at Lowe's that is made by "Oatey" called "Pipe Seal" with the description "Seals soil pipes and joints". However, on the
Please complete the rest of your message, Cheers, Tom

Tom,
OK so my reply keeps getting cut off, maybe if I use the "answer" section it will give me more room... So to clarify, The Red material in the picture is the Oakum and the grey material is the lead substitute? I have a product I found at Lowe's that is made by "Oatey" called "Pipe Seal" with the description "Seals soil pipes and joints". However on the back of the can is says "not recommended for plastic pipe". Am I better off hunting down the Harvey's Soil Seal you sent me a picture of? I'm a little wary about getting the sealant around the bottom of the fitting because there is only a 1" space underneath the tee nose to work with. When you say "I'll need room to lever the PVC", do you mean that the donut will fit so snugly inside the cast iron and around the PVC that it will not go in by hand? So if I devise a ratchet or lever system to push it in place, I'll be OK. Thank you for taking the time to help me!