I want to add a 3 inch y to my existing 3.5 inch cast system , is there a way to do it that keeps the mainline 3.5 inch ID

There is not, and never has been, a 3 1/2" cast iron pipe size. It is even rare in steel piping and was usually only used for steam heating systems.

Its amazing that people think they know everything. It is 4.25 outside dia, it is made of metal, once I find someone that knows what they are talking about, I will cut it open and send you a pic . That way you will be wiser and maybe not so arrogant next time, Apparently there is 3.5 PVC so I will look for that at the wholesaler.Thats unless someone that truly knows about my pipe and could give me a better idea.

In the USA you will look a LONG time before you find a piece of 3 1/2" PVC, and NEVER a piece of steel 3 1/2". How long have you been doing plumbing that you are so wise. I am basing my answer on 60+ years doing it.And once you DO find that 3 1/2" PVC, where are you going to find a "sanitary Y" to fit it?



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everybody calm down....it's just pipes. lol

I am not a plumber and if I can find the 3.5 inch pvc, I am sure they would have the fittings too. now as a 60yr plumber, what would you do to tie into my pipe, size up to 4" abs Y or restrict it down to a 3 inch, either would cause a bulge in or out. I have found the ID by reading another post that said he had cast pipe that was 4.25 OD and the ID was 3.5

Service weight cast iron has an OD of 4.3". Could that be what you have?

That must be right, how to best connect into it with abs Y

prefab your wye with two 6" cut pieces glued and set into the wye.
measure that entire length. Add almost a half inch to that measurement
and remove that much of the existing CI pipe. with the appropriate
CI to plastic shielded band make the connection by sliding the metal
portion back onto the CI and rolling the rubber onto your ABS stubs.
grade the wye past level and tighten to 60 in/lbs of torque.

Quote

...he had cast pipe that was 4.25 OD and the ID was 3.5

That would be nominal 4" service weight cast iron.

see advice just above

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

you cut in a cast iron "Y" using no hub couplings and transition to plastic at the branch of the "Y"..

I would have to see it. You will NEVER find any drain fittings for 3 1/2" pipe, regardless of what you THINK. However, I would use a 4" No-Hub cast iron Y, (which has a 3.94 id and 4.30 o.d.) rather than a plastic one which will have a 4" i.d and 4.50 o.d.



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hj, guess what???
in MA it is illegal to add a plastic fitting into a cast iron stack. must use 'like' material. so, we are required by code to use a cast iron fitting when adding to a cast iron stack.

Here, you can make ONE transition between materials, but then have to continue with the new one. However, since it is almost easier to install a cast iron tee, in any material, that is what I would choose to do. But if he is going to insist on working with 3 1/2" material, there is no hope for dissuading him. As Bull Halsey said, "Damn the torpedoes, full speed ahead".



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I am just going on internet info to arrive at 3.5 inch ID, now I am wondering if its just thin wall 4 inch cast, that would make more sense being 4.3inch OD, will need to be prepared for anything since I am cutting into the mainline going to the road and the house will be out of order until its done, hopefully I can just add a 4 inch Y and continue from there. What do you people think I should run to my toilet through the slab, 4 inch or reduce it to 3 inch. Is there an advantage to keeping it 4 inch , I am also adding a washer, bath and kitchen sink on the same line. Thank you

run 3 inch below the slab. it will be more than adequate.
when you get to the toilet, use a 4 x 3 elbow with the 4 inch facing up. stick a piece of 4 inch plastic out of the floor a few inches. then pour the slab and tile the floor right up against the pipe sticking out of the floor. for finish, get a flange that fits inside 4 inch pipe. cut the stub flush with the floor and glue the flange inside the pipe so it sits on the floor.
by the way, when you cut out a piece of your underground pipe, cut it carefully so if you run into a problem with sizes you can just re-install the piece you cut with rubber couplings. better to be safe..

yes I would do what packy says to cut it with a cast iron blade and make a nice square cut, I found that putting a hose clamp all the way around really helps to make a nice guide for that. If you make two square cuts you have the mending piece you need in an "emergency" situation. I will say if you CI pipes are very old you may be suprised when you look in the inside it may be corroded and with debris buildup over the years you may not see the round "ID" anymore but more like the inside of a cave.

^ don't play with the stalagmites.

and don't stand under stalactites.

if I find it like a cave, should I flush it with a high pressure hose or will that just cause it to pile up and clog, drain cleaner ??, I am only about 20 feet from the city pipe and 25 feet pipe going into the house from cut

Quote

...you cut in a cast iron "Y" using no hub couplings and transition to plastic at the branch of the "Y"...

DITTO

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

The stalagmites and stalactites will be metal and there is almost nothing, other than high powered equipment, which will remove them.

If Bull Halsey said that, he was quoting Admiral David Farragut at the battle of Mobile Bay. (I am just now reading a biography of him.)

its not really a cave and your stalactites are sludge , how best to clean it out

if it drains ok leave it alone

the 'sludge' may be holding the piping together



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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

The original corrosion forms as the metal oxidizes in the presence of moisture, but after it forms the layer of corrosion, it stops, leaving the underlying metal intact. Removing all that corrosion(provided you could) would simply leave the intact metal prone to oxidation and weakening the pipes.

There is a way to rim you CI pipe. It requires special equipment using a high pressure jetter with a chain flail cutting head.

I am not a plumber just a DIYer but two years ago I had this done to my CI lines and I had a few threads discussing it with pics. Here is such a thread.

[www.plbg.com]

It was a job over $2000 which I later on regret doing. There were so many things that went wrong with that job...but that's about right with almost every experience I had with hiring out plumbing work in South Florida.

Sum with you not being a plumber I want to thank you as you've shared a lot of your experiences with us and most of us have learned something if not a lot from reading your posts. Thank you.

vic thanks for the kind words I am not sure there is much to learn from me except what NOT to do or don't hire who Sum hired LOL!