I know what it is and where it should go, I've done enough of them
Yes Mike it's the pick up for the back of the tank which is a lot lower than where the pump fits
As Mike says above the arm goes toward the back of the tank at an angle,the edge of the square end fits in the rectangular cream piece in the bottom of the tank that you can see in the picture.
It takes a bit of trial and error if you've not done it before but once you get it in the right spot it all fits
Russ