In-line HEPA filter?

Hey hey, quick question. I've been using an aquarium pump/airstone combo for my starters lately and have heard talk of using an in-line HEPA filter to keep the air that's going into the starter clean... Sofar I haven't had any problems with infection, but I guess I'd rather be safe than sorry. Problem is, I can't really find a whole lot of information about this type of filter anywhere....

Anybody know anything more about these? Thanks in advance!

Guess I was relying too much on a Google search. Thanks!