Unlike other sterilisers, this unit has three inlet / outlet's - very useful if you want to run the output to a two-fall waterfall, or indeed a waterfall and a filter. The unit comes complete with three stepped hosetails to fit a variety of hose sizes.The sterilizer is also supplied with a separate glass viewport which can be used to replace one of the hosetails for use as a one-in / one-out unit.This model comes with an external ballast.