Leftover parts from Elos System MIDI 36gal

I had a few pieces I wasn't sure where they go or what they were after setting up my Elos System MIDI 36gal. The slanted round PVC piece I just found out goes into the overflow entrance at the top of the display tank.

However, I am not sure what the two identical screw in "nozzles" with rubber O-rings are for. Also, I am not sure what the rectangular plastic piece with the corner cutout is for. Lastly, I am also not sure what the other plastic piece with the circular hole in the middle is for as well.

Thanks,
-Jonathan