If the wastewater is from a non-domestic source, pretreatment other than a septic tank may be required if the influent to the Gravel Filter is not within the allowable limits for recirculating gravel filters. Wastewater Distribution Pressure distribution: Pressure distribution with timed dosing is required and must comply with the pressure distribution standards and guidance. This requirement applies to all pressure distribution related components. Wastewater application to the filter bed: The wastewater must be applied to the layer of drain rock atop the filter media, or sprayed upward against the top of gravelless chambers.