A reductant dosing system for an engine is disclosed. The reductant dosing system may have a supply of reductant, a reservoir configured to hold pressurized reductant, and a pump configured to draw reductant from the supply and discharge reductant at an elevated pressure into the reservoir. The reductant dosing system may also have a plurality of injectors fluidly connected to the reservoir, and a drain valve fluidly connected between the reservoir and the supply.