Our old 2" cast iron drain got plugged up. Rented a 40' drain snake. It stopped 20' in. Still had water on the floor. Rented a jack-hammer and removed 35' of 2" cast iron pipe. I have exposed the 4" cast iron main line. There is a 'Y' to the 2" line. I left about three feet if the old 2" pipe in place.

I would like to put 3" ABS in to replace the 2" cast iron. Should i cut out the old 4" x 2" 'Y' and replace it with a new ABS 4" x 3" 'Y'? Or leave the 4" main line in place and reduce from 3" ABS to 2" cast iron just before the 'Y' and connect with a shielded no hub connector?

What is the best way to cut the cast iron pipe? Will a sawzall cut a 4" cast iron pipe very easily?

I have done allot of plumbing, just not much underground. I have most of the tools I need.

Hi Martin...

Replace the 4" x 2" wye with a new 4" x 3" wye fitting... and here's why.

Say years from now you've sold the house and that 2" drain that you left underground clogs up and someone goes to snake the 3" drain line you installed using a large snake head and the snake head gets caught in the 2" drain line... could cause all kinds of issues including having to chop up the floor and remove everything you left behind!

Use a sawzall with a DIAMOND sawzall blade (only sold by Lennox) if possible. Otherwise, a carbide tipped or even a 8-10 teeth per inch bi-metal sawzall blade will work fine.

Here's a link that shows some good info. on working with old underground:

https://www.askmehelpdesk.com/plumbing/new-basment-bathroom-252241.html#post1244996

You don't need to read the whole thread... one of the longest on the plumbing page... but check it out and let us know if you have questions, OK?

You will want to purchase shielded transition clamps that go from cast iron to ABS plastic pipe to install the wye fitting.

Mark