Anyone know how to separate old pushfit (plastic) soil pipe fittings ?

[Skylark]

I'm going to have to remove an old Rymway (see my other post ) pushfit fitting from the 110mm stack in my bathroom in order that i can replace it with a more modern fitting that can take a 40mm boss adapter however space is tight and the branch is stuck fast and not willing to pull out.....any ideas on how to ease it out appreciated
thanks in advance
Skylark

 

[Ted808]

Have you considered cutting with cheese wire?
Then replacing section of stack with slip couplings and your boss?

 

[Skylark]

Thanks ..But i've now decided to replace the whole stack with metric branches incorporating the bosses i need at the places i need them unk: ...........Gonna remember that cheesewire tip tho !