A multi-container manual-pump-operated backpack sprayer including an open-topped backpack enclosure, a plurality (preferably three) modular liquid containers removably seated in the enclosure, a hand-lever-operated pump/accumulator combination, and a user-controllable manifold for selecting a particular chemical from the containers for administration through a spray wand. Chemical is carried to the pressure chamber by manually pumping. The pump draws liquid from a manifold-selected supply container outward through tubes to the manifold, which has a console of valves. Separate return tubes are provided for each chemical from the manifold back to the containers of origin, and the manifold allows convenient flushing of each chemical back to its container of origin. This ensures that chemicals are not mixed or cross-contaminated and avoids waste since all residual is returned back to its respective container. The manifold is conveniently carried at the hip for ease of access.