Fluid Drainage System with Textured Core Sheets

A wastewater treatment system includes a cavity configured to receive a flow of wastewater for treatment. One or more core sheets are arranged within the cavity in a position to be contacted by wastewater entering the cavity. The core sheet has a primary textured surface enhances retention of wastewater fluid received by the unit, which over time causes an increase in build-up of biomatter on the surface, which in turn enhances the efficacy of treatment of the wastewater. One or more sheets of fabric may be used with the core sheet. The cavity may be within an aerobic treatment unit (ATU).