This is Atlantic Water Garden's Pump Vault Extension. We have a large selection of Filtration and other pond and water garden supplies from Atlantic Water Gardens.
Manufacturer's Description
The heavy-duty one piece design of Atlantic's Pump Vaults can accommodate large pumps and flow rates. Features include large openings for pump access, cut lines for pump discharge and pipe extensions, and flat panels for custom plumbing. Multiple extensions can be added to increase the height for installations that require a deeper basin or greater water volumes. The depth of a pond-free basin can be increased by one Eco-Blox for each added Pump Vault Extension.