Planted Tank Enthusiast
Join Date: Aug 2008
Location: Long Island and Queens
its cascading, so there is an overflow into the media section, the first compartment, and then it either overflows, or fills from the bottom into the pump section. so both have water. its basically an overflow box if you want to google how those work.
**I personally don't have one, so if anyone else with actual experience needs to correct me, please do.