water filter

I bought one of these to attach to my hand pump..
This is likely a a dumb question, but how many of these little discs are you supposed to put inside the tube? Are they meant to be crammed in there till it's full, or does one or 2 discs do the job? I have 3 or 4 in there, but it seems to be harder to pump now, so maybe all I am doing is blocking the air..

I'd appreciate any feedback.

water filter.jpg