non threaded pipe for return lines

[Melnic]

So,
the Pool guys did not re-install the return fittings.
The pipe at the pool wall is NOT threaded. These just plop in there. 2 of them had some sort of rubber tape on them. Last year, one of them kept popping out.
I have 4 of them and I would like to get something new.

Suggestions?

(adding pics)

 

[kadavis]

https://www.poolpartsonline.com/p-71866-aussie-insider-fitting.aspx