I have fitted “top hat connectors” successfully many times when presented with a flat surface and clay pot liner (assuming a successful smoke test as outlined in building regulations).
However I have had a major problem with one recently – see below:
Okay so this is all very normal. But the one pictured developed a condensation leak (condensation mixed with tar). See pic below.
I removed it and re-fitted it. But it leaked again, even though I bedded the connector onto a thin bed of mortar. On the second attempt tar even leaked from one of the screws.
So I fitted one of these: a sump adaptor