schnzerlover, the original post is from 2004.
They were also talking about a 20 gallon tall, not a normal 20 gallon long. A 20tall wouldn't really have adequate ventilation for a rat.
Tanks in general are actually kind of bad for rats because of lack of ventilation - ammonnia fumes can build up really quick and cause respiritory problems, especially with wood shavings, but even with other types of bedding.
The best housing for a rat is a rodent cage, with a solid floor (their feet can get caught on wire), and places to climb.
I housed both my rats in tanks, but they were almost never in their tank, they were always out at least 8 hours a day on leash or running around playing, and the bedding still had to be changed very frequently.
I'd also like to mention that they're much happier in pairs because of how social they are - though they can be happy by themselves if given constant attention.