
My last post got drowned out by newer ones (no pun intended) after I had updated it with actual pictures of what's in the drain:
https://i.imgur.com/A2R2UmL.jpeg
https://i.imgur.com/yb6rbqM.jpeg
https://i.imgur.com/KS0IUte.jpeg
https://i.imgur.com/82lgbpm.jpeg
AI is telling me that it's to stop sewerage gases when there's no P trap - given it's on the 2nd level above a garage, this could be possible? But, there's no sealant in the drain where it pops back in, so I don't think it would do a good job. There are no sewerage smells in the ensuite at any time.