K-Holed
Fishaholic
I personally would pass laws to stop this method being used. When this type of filter goes wrong it involves a huge amount of work and mess. To add to the negative the gravel must be kept clean at all times and that takes about an hour to to every week. DON'T USE THIS METHOD
A touch harsh on the old UG filter I feel. All my tanks used to run on UG filers and the maintanence was minimal. My LFS used to run all their tanks on UG filters too, it's still a very good form of biological filteration and the gravel can be cleaned in the time it takes you to do a water change.
Just my opinion.