I'm confused. I think you're using the word "filter" when you really mean "filter media." The filter is the entire machine that does the filtration. The filter media is the sponge on which your good bacteria live. Anyway, see this thread because it talks about how to jumpstart a new biological filter (good bacteria) with an old tank/filter and media
http://www.aquariacentral.com/forums/showthread.php?t=82295
Also, using water from an established tank will not help your tank, because most of the nitrifying bacteria reside on surfaces. Things like bio-sponges, foam, and ceramic rings are great biological filter media because they have massive amounts of surface area, so will have relatively greater numbers of bacteria than anything else in your tank.
If you want to borrow some bacteria from your friend's tank, would he let you have his old filter sponge? He would still have enough bacteria in his gravel and tank that he probably won't notice a change. Otherwise, you could just take his filter sponge and squeeze the gunk into your tank. The bacteria will float around for awhile in the water, until they settle onto surfaces. So you might see cloudiness in the first few days which will be the bloom of beneficial bacteria.
Yes, gunk will clog your filter sponge. This is not good because it impedes the flow of water, hence reducing effectiveness of your filtration and suffocating your good bacteria. They need oxygen to do what they do, which is supplied by adequate flow of fresh water. To prevent the clogging of the filter sponge, you need mechanical filter media. This is usually cottony like filter floss, or the white bags you usually get in packs designed for your filter model. This mechanical filter media must be placed in the filter in front of the biological filter media. This way, water will pass through it first, particles will be trapped on it, allowing only water to continue through the bio-sponge.
For more examples of the various types of filter media, check out
http://www.drsfostersmith.com/product/NavResults.cfm?N=2004+113803
It's where I buy most of my supplies from. On that page, there is also articles about the different kinds of filtration: mechanical, chemical, and biological. Just so you know, I don't find a need for chemical filtration. I do water changes often enough that I remove the things that chemical filtration media claim to.
hope that helps, I know it's a lot to absorb. You'll find that once you feel comfortable with your aptitude as a fish-keeper, you'll also be somewhat of a water chemist! Good luck, Nick, and I look forward to seeing more of you around the forum
