40mm PVC pipe to 110mm cast waste pipe

[DIY Dad]

Hi folks, I'm new to the forums and looking for a wee bit of advice. Having recently bought a new home I've found a leak under the sink which needs repaired.

I have a 40mm PVC waste pipe going from the sink into a 110mm cast iron stack, which is packed with what I think is Plumbers Mate or something similar which is very soft and pliable (see photos):

Advice from the guy in a local plumbers merchant is to dig out the sealant and repack it with Plumbers Mate, Putty or even silicone ...is there any other simpler solution, like some kind of reducer to connect the cast to the PVC?

Any help is greatly appreciated

 

[ShaunCorbs]

What is the dia of the cast looks more like 2.5-3" ??

 

[DIY Dad]

What is the dia of the cast

It's definitely 110mm ...4 1/3"

 

[ShaunCorbs]

McAlpine DC2BL-OS Offset Drain Reducer Connector - Black: Amazon.co.uk: DIY & Tools

 

[DIY Dad]

McAlpine DC2BL-OS Offset Drain Reducer Connector - Black: Amazon.co.uk: DIY & Tools

Shaun, thanks a bunch
Cheers

 

[snowhead]

There will be a piece of copper or lead into that cast iron with the plastic connector onto it. I bet the condensate from the boiler hasn't helped.
If that's 40mm plastic, then it's not 4" internal cast, it'll be 2.5 / 3 as Shaun said.
The collar on the cast is about 15mm thick.

You may end up using something like this, sizes would need confirming first over the outside of the cast;
Fernco Adaptor Coupling 112-102 / 45-38mm Grey | Priority Plumbing