External pipe from shower has popped out!

[SBrad]

so, just noticed water leaking outside and realised someone was in the shower! Then looked up and saw...(see attached photo) that the pipe from the shower had popped out at the joint. Now, it looks like it’s been that way for a long time, but I have not noticed water coming from the pipe or had lots of water on the ground.
Do I need a new pip section? Can I just clean the bit that fits inside the down pipe and pop it back in? Is there a rubber seal I’ll need to replace?!?
Grateful for any help and advice!

 

[denso13]

It may need a new rubber boss adapter but give it all a good clean and it might all pop back in ok. The trouble is that the connecting waste is all push fit and can move in the heat and cold.

 

[SBrad]

Thanks very much!

That is very helpful!