No such thing as a dumb question
You only need the floss part of the filter. If you have one that the floss "slips" over the plastic, then you dump in the carbon, pull the plastic out and simply cut the fabric in half (or to "size"). Then put it behind the filter in the 5g. If it's one of the blue ones that is "attached" to the plastic, just cut it off and place it behind. Be sure to knock off any loose carbon pieces so they don't get into your impeller and mess it up.
The bacteria will attach itself to the filter in the 5g and.....VIOLA instant cycle. Now, with a 5g, you will have more trouble keeping it cycled when you remove the filter for changing. Do this everytime you change your filter, and no worries. I have a 10g fry tank that I do this too, and it has never recycled, even though I change the filter every 2 weeks or so. It's amazing how dirty fry can be
I'm glad to here you have good housing for the Clown. They are my BABIES, so I get kind of protective of them on a general basis
I know of people who have them and they have grown to 8 or 10 inches. So, just realize they can get that big. They are slow growers, but also live for MANY years.