Help! Aquael Ultramax 1500

[Dave Y]

Hey Folks,
Need some help with an Aquael Ultramax 1500. I was just giving it a clean out (it's been cleaned many times before). Just a normal clean, sponges, impeller etc. When putting it all back together I noticed what looks like a rubber non return valve in the bottom of the sink (images attached).
I just can't figure out where it came from!!
The filter won't run properly without it - does anyone know where it might go on this filter?
The only exploded diagrams I can find are useless.

Thanks
Dave

 

[Andy Taylor]

That looks like the flap thats inside the pre-filter if i remember rightly

 

[Dave Y]

Ahh yes, thank you!!
Right at the bottom of the pre filter housing, probably the only place I hadn't looked.