Ultra Reef Overflow OutletsUltra Reef over flow outlets and Returns which fit on the back or side panel of your aquarium instead of having an internal weir box this buys you more space in the main tank. These allow you to take water from your main aquarium and drain it to a sump. 1 sizes available for both drain and returns which are bought separate So you need to buy 1 x drain and 1 x return or you can mix and match with 2 drains and one return or 2 returns and 3 drains the