A system for supplying a processing solution to a printing device, such as a photographic processor or a printer, which includes a supply tank with processing solution or ink and a delivery system between the supply tank and a printing device. The delivery system has a retaining vessel with retained fluid, in the vessel, and a reference probe to signal a level probe when fluid reaches a predetermined level on receipt of a replenish signal from the controller for the printing device. The power supply actuates a three-way valve in order to flow a volume of the processing solution from the supply tank to the retaining vessel. A power supply receives the adjustable liquid level probe signal from the adjustable liquid level probe. Then switches the three-way valve to flow the retained fluid from the retaining vessel to the printer.