Hello, I have a problem. I have a 62 year old house with a rotting buried Sewer pipe made of cast iron. It actually broke, creating a huge sink hole in my front yard. The broken piece is actually the bell of a "Y" pipe and the section is about 3-4 feet long. How would I go about replacing this broken piece of pipe, and with what? Cast? ABS?

Remove enough dirt so that you have access to the pipe, make a couple of cuts and replace the pipe with a piece of PVC and shielded couplings.

Use ABS or PVC, whichever is popular in your area. If you use couplings with stainless steel couplings get ones intended for a cast iron to plastic transition. Outside the building and buried you could also use the all rubber unshielded type. If the wye is capped off on one side and it is an appropriate location you might want to bring a line up to the surface for use as a clean-out as long as you are out there digging.

Can I use the rubber boot coupling underground?

As a matter of fact, it DID have a clean out attached to the "Y" pipe, but, it was buried 4 feet underground and was unknown as to its existence and was completely unaccessible. The problem is that The rest of the cast seems to be in good condition. I do not really want to dig up the rest of my yard if I do not have to. Does anyone know what the code in Southern California is?

The rubber couplings are legal in california if they are buried outside the building. The shielded couplings are better, but probably a little harder to use for a novice. Bringing a clean-out to the surface is for your convenience, if you ever need it it will look good.