pipeplumbingsewer
I have these caps just outside of my house that I’m assuming are sewer clean outs. The problem is the pipe is all corroded and the caps are PVC that are just set on top of it. They don’t seal as there are no more threads.
Do I have to completely dig out the access and replace with PVC, or is there another way to attach to the metal and seal near the surface?
What’s the best way to remediate this so I have a seal?
Here's my speculation, based on your description and my experience. It is just a theory. Do not commit any resources based on this without collecting corroborating physical evidence supporting it. A direction to investigate at least.
The main floor plumbing goes out to a septic tank. The pipes were not placed lower because there was no need, it just meant digging deeper outside. No one wants to do that without good reason.
When the city sewer was installed, the basement construction tied into it, but the old plumbing was never redirected, it remained on the septic tank. Not the best scheme and possibly illegal, but I'm not surprised someone did this.
It is highly probable there is nothing below to the basement to tie into. The sewer may not be much lower than the basement drainage exit. Anything placed lower than this will likely need to drain into an ejector pumping chamber.
If the pipe itself is in good enough shape, you could just use a compression cleanout plug (sometimes called a mechanical cleanout plug) or a pressure testing plug:
There are quite a few different styles of these, but almost all of them work by compressing and expanding a rubber gasket inside the pipe. 2.5" might be hard to find at the big box stores, but they are available numerous places online. The main consideration would be finding one that would seat deep enough into the pipe that it would be beyond the notches for the old cap.
Best Answer
A common approach is a rubber coupling (also called a "Fernco®" for the same reason adhesive bandages are called "Band-Aids®")
Counter-intuitively, the last time I read the instructions carefully the ones with a stainless steel reinforcement (sheilded) were not recommended for burial and the plain rubber ones (unsheilded) (with stainless steel clamps) were, but read the instructions carefully yourself to be sure.
General approach is to cut off the iron pipe and use a rubber fitting to transition to PVC. Then be sure to protect the PVC from sunlight (cover it in some way, or at the least paint it. Sunlight is not good for PVC pipe.) You may need to use a wire brush and/or grinder to get the outside of the iron pipe smooth enough for a good seal.