A spray combining apparatus for use at the outlet of a fluid collection system (10) includes an outlet pipe (11) containing a diffuser and atomizer (15) adjacent an outlet opening (18). A conical rain cap (19) is mounted vertically above the outlet opening. A downwardly-facing nipple and spray nozzle (22) is positioned above the rain cap. The nozzle is supplied with a pressurized second fluid from a source (26). If first fluid is detected in the outlet, the second fluid is discharged through the spray nozzle in a selected enveloping pattern toward the outlet. As the atomized first fluid is emitted from the outlet opening, it is combined with the enveloping spray of the second fluid. The resulting neutralized or "washed" product is either suspended in the air, or is contained in the vicinity of the outlet.