Putting a bog in a room that used to have one should be a simple task,
you'd think.
(In a shop premises we took on a couple of years ago, upstairs gutted
and largely derelict)

I decided to run a new mains water pipe, shoved the pan into the soil
pipe, flushed, plainly a blockage.
The soil pipe had been 'capped' with tea towels which I removed (I know,
what a ###ing pro) so my concern was that one had traveled.

Much plunging later and we were flushing, game on. Except the flush was
going into the ceiling below What a mess!

Long story short, there were 2 pipes bossed into the soil stack*, left
open when the place had been gutted and upon cutting out this section
there was a dishcloth just slightly downstream of the above restricting
the downward flow.

So my advice would be to replace a soil stack (or sections of) that has
anything of unknown provenance bossed into it.


*Not immediately obvious, they were bossed into the rear.