If you are one those people that tries to clean aquarium equipment thoroughly, you need some of these. Nothing else can really successfully clean things like the inflow tubes for overflow filters. If you're adventurous enough to have taken heaters apart (to made one good one out of multiple bad one, or whatever) these also work great for inside them.

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[updated on 2008-02-28 00:13:44]:
This was supposed to be a 5. I've become fanatical about making sure I click the right number several times but this still occasionally happens.??????

Pros: Makes cleaning easier

Cons: none

I like this set of brushes to help clean all the little parts of the filter system. It would help to have a really flexible one in addition to use in the filter piping that makes the U turn at the top part of the filter.
I have also used pipe cleaners to help out. Good tools and you really need them.

Pros: A must have

Cons: none