antisiphon valve

[chart]

What is the object next to the valve sitting on top of the tank?

[tsubaki]

That "was" the filter screen.
Depending on the tank manufacturer, the fitting may be pressed into the tank and almost not removable. See if the hose connection unscrews from the tank fitting, that should be the anti-siphon.
You may have a screen filter in the tank at the end of the pickup tube.