provided with suitable check valve means to prevent back flow of air and entrained material from vessel 20 into separator 142 the check valve means employed in the invention comprises a 90 u00b0 elbow 156 positioned at the lower end of stand pipe leg 154 a flapper valve is mounted on the discharge end of this elbow in the form of a flat baffle plate 158 which has wings 160 projecting from its outer sides to form supports for pin 162 that extends through apertures in this baffle and through tube 164 carried by plate 166 vessel 20 is surrounded at its lower extremity by circular header 25 from which depend a plurality of nipples that connect to nozzles 170 which extend through the side wall of the vessel 20 these nozzles can be threaded and bear from their inboard ends elbows 172 and associated water jet nozzles 174 which are directed downwardly and outwardly to spray against the side wall of the vessel facilitating washing of accumulated debris from the side walls during cleaning of the vessel a total of eight of these nozzles can be provided at 45 degree centers about the periphery of vessel 20 to insure adequate washing of the interior side wall and bottom of this vessel the exhaust gas treatment and muffler facilities contained with vessel 40 are shown in fig1 and 12 as there illustrated vessel 40 is similar in construction.