The Eshopps WD-100CS wet/dry filter is a complete filtration package; including a classic Wet/Dry type fitler system; and a Hang-On Overflow box; for aquariums up to 100 gallons. This combination is ideal for providing enhanced biological filtration for your freshwater or marine fish aquarium. The filter uses a replaceable felt filter pad; that sits in the drip tray for mechanical filtration; and has a seperate chamber to house a return pump (not included). For aquariums that do not have a drilled overflow system; the included compact U-tube style overflow box allows for installation on virtually any aquarium. The Hang-On overflow is only 3" wide; minimizing the space required between your tank and wall. The system includes a 3' drain line and a length of vinyl tubing with a valve for return lines; all you need to supply is an appropriate return pump to get up and running.