Reefkeeping Basics by Greg Taylor  Everything You Always Wanted
to Know About Sumps, Part I  The American Heritage® Dictionary
of the English Language, Fourth Edition defines a sump as:  A
low-lying place, such as a pit, that receives drainage.  This is
an accurate, albeit simplistic description of an aquarium sump.
Tailoring the definition a bit to be more descriptive of our
usage of the word in the hobby it would read:  A tank or
container placed lower than, and which receives drainage from,
the display aquarium.  The obvious first question most beginners
have is, "Why in the world would I want one of these? They add
more complexity and possibilities for disaster, don't they?"
Well, if installed correctly, the many benefits to installing a
sump on your aquarium far outweigh any of the few downsides.
The benefits include:  · increasing total water volume, ·
providing a place for equipment and filtration, · keeping the
surface of the water free of contaminates, · aerating the water,
· simplifying water chang