Drilling a cast iron soil stack?

28 Jul 2008
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United Kingdom
Hope someone can help.. I am relocating the bathroom and need to connect into the existing cast iron soil stack.
The cast iron soil stack is 4".
My questions are.... Can I drill the cast iron SS to fit 32mm & 40mm strap on PLASTIC bosses?
Also can I drill the cast iron SS to fit the WC waste either 110mm(4") or I believe there is an 82mm(3") strap on PLASTIC boss?
Please Help.
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Can I drill the cast iron SS to fit 32mm & 40mm strap on PLASTIC bosses?
About 95% of them leak, I wouldn't try it any more.

can I drill the cast iron SS to fit the WC waste
NO. Cut a length of SS out and insert a plastic piece to join to. There are also Fermco rubber couplings which are OK but look horrible!
Thanks for the prompt reply Chris. Could you tell me more about connecting the WC to the soil stack. ie.. Why doesn't the soil stack collapse when I cut a section out? How do I support the soil stack? lastly, what is the name of the fitting that fits into the section that was cut-out?
Thanks Jason
i always fit one of these in to the cast stack then carry on in plastic
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Sorry lads.... have you heard that the soil stack can be a minimum of 75mm internal(82mm external).. I have a JTL plumbing book that says you can. So to clarify.... can I reduce to 82mm soil pipe... then drill the cast iron...then place in the imaginary 82mm strap on boss that I can't find!!!! Jason.
but then your just causing problems for yourself.
as you will have to get a pan connector that fits the reduced size not as common as a 110mm pan connector
i've not seen that size strap on boss.
You can buy from drain center a metal boss designed for cast stacks.....40mm only but you can insert a rubber reducer to 32mm........downside.....35 quid each and that was 2 years ago......you need a 50? 54mm......bi metal hole saw tho.......can't quite remember which one.......probably easier than cutting out a section
The commonest solutions are probably
1) change the entire stack to plastic, which is not as daunting as it may seem
2) Use one timesaver coupling to convert to plastic, often for the whole lower section
3) use 2 timesaver couplings to replace a length.
They look like this:

View media item 3255
Thank you all for the advice.
You have been very helpful and prompt.
I have decided to go with..... wait for it.....
Chop the stack and replace with plastic.
Thanks again


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