Hello Earache,

This is a filter assy. The ball valve on the top
is use to flush the filter. The top of this is removable.
By removing the top you can clean the unit more thoroughly
and inspect the filter itself. Don't be confused if the
inside does not look like a filter but more like a bunch
of ribbed rings held together (it is still a filter).

Avoid using pliers if you can
Dry conditions and a good grip should remove it with ease.