A precursor source vessel comprises a vessel body, a passage within the vessel body, and a valve attached to a surface of the body. An internal chamber is adapted to contain a chemical reactant, and the passage extends from outside the body to the chamber. The valve regulates flow through the passage. The vessel has inlet and outlet valves, and optionally a vent valve for venting internal gas. An external gas panel can include at least one valve fluidly interposed between the outlet valve and a substrate reaction chamber. Gas panel valves can each be positioned along a plane that is generally parallel to, and no more than about 10.0 cm from, a flat surface of the vessel. Filters in a vessel lid or wall filter gas flow through the vessel's valves. A quick-connection assembly allows fast and easy connection of the vessel to a gas panel.