The invention provides an apparatus and method for removing diatomaceous earth and contaminants from a filter and for filtering liquid using diatomaceous earth. Embodiments of the method can include a washdown process, a backwash process, and a filtering process. Some embodiments of the apparatus can include one or more filter cartridges with cartridge tubes to increase flow during the backwash process. Some embodiments of the apparatus can include a backwash sprayer to disturb contaminants during the backwash process. Some embodiments of the apparatus can include a removable lid to access the filter cartridges during the washdown process.