Cast iron toilet stack
I am currently trying to refit bathroom floor which meant removing the toilet. The toilet ran into a flexi connector which ran into the old cast iron waste stack going into the wall.
On removing the toilet the old flexi ripped so I am trying to replace it.
The diameter for the cast iron stack is approx 160mm wide funnelling down to approx 120mm. I cannot seem to find any flexi pan connectors which can now accommodate this size. What do I do?
Advice from 4 local tradespeople
This is a very common issue when dealing with older cast iron soil stacks.
Flexible pan connectors are generally not designed to seal directly into cast iron, especially where the internal diameter is irregular or flared, as in your case. This is why you are struggling to find a suitable flexi connector to fit properly.
The correct solution is to use a cast iron to plastic adaptor, often called a CI to PVC soil adaptor or a rubber compression adaptor. This type of fitting is designed to clamp securely onto the cast iron pipe and provide a standard 110mm plastic outlet that a modern pan connector can then connect to.
In some cases, the cast iron opening may need to be cleaned back thoroughly and measured accurately, as old stacks can vary in size. A rubber adaptor with a wide tolerance range is usually required.
If the cast iron is badly corroded, cracked, or out of shape, the best long-term solution may be to cut back the cast iron stack and convert to plastic at a suitable point using a proper conversion coupling.
Avoid using sealant alone or improvised fixes, as these will almost certainly leak over time. Using the correct adaptor will give you a secure, serviceable, and regulation-compliant connection.
In this instance I personally would source one 160mm coupling reducer from 160mm to 120mm and fix this in place to the old cast iron stack and then cut a piece of osma drainage pipe to insert and then connect to to a flexipipe designed to attach to a toilet and also the osma pipe
I would suggest cutting the cast iron stack from the outside of the building and replacing the removed stack in plastic. Future proofs any further adjustments you may make to the toilet.
You may require a rubber reducer like the one below, or similar.
https://amzn.eu/d/iTE3t3v
