i.e. generic in the sense of applicable or referring to a whole class or group (essentially general rather than specific), thus allowing for broader patent protection. (In patent language, "Gattung" refers to the generic class under which an invention is classified). So, the basic patent will be for a very general filter, without using too many specific terms that would narrow or restrict the protection offered by the patent.

In what ways could the parts (steps) be changed or equivalent parts substituted without changing the basic invention?
Is there a generic description for any of the parts you listed (i.e. "fastener" instead of "Machine Screw", or "plastic" instead of "polypropylene")?
http://www.bpmlegal.com/pdisfm.html

PATENT FILING STRATEGY
file a generic patent application for the broad concept with the risk that without specific examples it may not get granted: this can act as a deterrent until you file a more specific patent application (perhaps directed towards a selection invention) for the best embodiment of the invention;
http://www.jaws.co.nz/media/patent-filing-strategy-timing-is...

The generic method is developed according to a first aspect of the invention in that
Das gattungsbildende Verfahren wird gemäß einem ersten Aspekt der vorliegenden Erfindung dadurch weitergebildet
http://www.wipo.int/pctdb/en/wo.jsp?WO=2000074917