2003 Compass waste pipe size

Hi all

I have our van stored a few miles away so cannot check myself easily

What size waste pipe should this have ?

While across doing some bits and bobs I checked the waste pipe received with the van but its to small but forgot to measure the size of the outlet

Anyone know what size it should be? id or od , I would like to make up a two into one fitting for the two wastes but don't know the correct size