Combined waste to stack query

[Adrian_P]

Hi. I wish to combine the wastes from my bath and shower (Both 40mm) at the point they go out through the wall, then a 1.5 - 2 meter run externally across to the soil stack, with the 32mm sink waste dropping in about 250mm from soil pipe. Do I have to use 50mm waste externally for this? Not may places seem to sell the 50mm black pipe and fittings. (SF do some 50mm in white and TS very little at all). Thanks in advance.

 

[Last Plumber]

Can the 32mm not go straight into the stack as well?
Using a strap on boss?

 

[Harvest Fields]

Wolseley normally have 2” black solvent weld on the shelf. I have picked some up today. Hope this helps.