Yes, the 110mm soil stack pipe. Didn't use an AAV, just capped it, the new soil stack does vent externally, the new stack & the old stack meet at a manhole outside, so hoped the old stack would vent via the new one when not under pressure & via the attached neighbours stack when under pressure?
A builder moved my bathroom some years ago put in a new external soil stack for the WC (all good). But, he left the old internal soil stack in place because the kitchen sink and washing machine emptied into it. Recently i removed most of the internal stack and capped it just above where the...