2' in the picture is the drain/bleed screw.
The drain nozzle is directly below it on the base of the assembly - you'll need to attach a length of tubing.
Edit - just to clarify, nothing comes out of the drain/bleed screw, it just opens/closes the nozzle below it.
I found it works best when ignition is left on as diesel is then under pressure in the filter if you decide to change it heres a utube video
YouTube
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