flow of the exhaust within the first second and third volume chambers 174 175 and 176 liquid and solid particulates are at least partially removed from the exhaust these collect in the bottom of chambers 174 175 and 176 a drain line and valve assembly such as assembly 112 shown in fig3 are added to the bottoms of each of chambers 174 175 and 176 to allow removal of any accumulated liquid and particulate solids therein the volumes of chambers 174 175 and 176 are sufficient to dampen spurious pressure excursions or pulsations to avoid damage to the catalyst elements 166 the exhaust exits the first volume chamber 174 through flow pipes 152 into the third volume chamber 176 the exhaust exits the second volume chamber 174 through flow pipes 153 into the third volume chamber 176 the exhaust exits the third volume chamber 176 through flow pipes 154 into the catalyst chamber or fourth volume chamber 178 the leading face of the catalyst elements 166 are spaced from the exit of the flow pipes 154 to allow a uniform flow of the exhaust across the face of the catalyst elements 166 to more fully utilize the available catalyst active sites in the catalyst elements 166 after the exhaust passes through the catalyst elements 166 the exhaust exits the fourth volume chamber 178 into the fifth volume chamber 179 through flow pipes 156 the exhaust then exits the fifth volume chamber 179 through the exhaust stack 160 which optionally has a flange as shown herein for attaching to a stack extension not shown the volume of the fourth volume chamber 178 and the volume of the fifth volume chamber 179 along with the volume of chambers 174 175 and 176 are to produce the silencing effects.