yes such seen many times in houses and bars...for the very reason that whoever put the tube work in at the start should have used 110 mm size tube when they used 90mm.....also many drains just descend from a great height..the correct gradient is 1:40 ...also look out for manhole access covered in dirt or worse concrete.

the trouble with drians is that once they go in its amost impossible to fix

ah yes, uninsulated, undersized piping and galvanized water tubes - two of the main plumbing headaches for houses built before the nineties.

The galvanized water tubes were always plonked in the ground for humidity and grit to eat away at them. Just a matter of time before they go.