In my basement, I'm eliminating the deep well for the house trap and cleanout, extending the pipes up to floor height and then filling with gravel topped with concrete. The house was built in 1967, so the waste pipes are cast iron.

I bought a 4" Fernco donut that says it fits DWV plastic (SCH40), SCH 40 steel, XH soil pipe.

The cleanout is 4" but had a 3" plug, I drilled out the lead, pulled the cast iron adapter and plug, and scraped out what was left of the oakum to get down to the pipe. When I insert the PVC wearing the donut into the cleanout, it slides in and is loose. The oakum was black rot, so I imagine that 50+ years of moisture also thinned the cast iron internally.

My last resort is to silicone around the donut to get a seal. The
PVC will be embedded in concrete, so it won't move once done, but I
really hate rigging things and want to do it properly.
So my questions are:

Is there a heavier duty donut that would fit better?

Is there a better fix?

Thanks, guys.

The cast iron did not "get thinner". You just have the wrong donut, assuming the cast iron was made to the specifications you are using.

What specifications?

I did research and now know what is meant by XH. A fitting on the waste stack says XH so I'm guessing they used XH fittings everywhere. Are you talking about that?

How old is the pipe? Originally, pipes were cast in molds and the specifications were very loose because lead and oakum could make any connection. Late pipes were spun cast and the dimensions were fairly constant. If yours are die cast, then the gasket may NOT be made to your pipe's specifications and will not work.



Edited 1 times.

oakum and 'rockite'.
pack the oakum with a big screwdriver, tapping it with a small hammer.
pack it tightly but leave a good couple of inches of space.
mix some 'rockite' a tiny bit soupy and pour it into the joint.
I would not do this above ground but since the pipe is being buried it will last a lifetime.
remember that like on a boat, the oakum will get wet, expand and seal the joint. the 'rockite' will give the joint strength.

if I'm mistaken about the joint and it is horizontal not vertical, just mix the 'rockite' firmer and pack it into the joint.

hj: the pipe is 52 years old.

packy: the cleanout comes up at 45 degrees from horizontal.

So am I correct in understanding that I would ditch the donut, insert the PVC to the bottom of the hub, then pack the oakum tightly around it (like it was cast iron), and use the Rockite in place of lead?

Also, is Rockite really different than hydraulic cement?

rockite and hydraulic cement are the same

yes, your assumption is correct.