An air/liquid separation system for an extraction cleaner, the extraction cleaner having a suction source for generating a working air stream and a fluid source for supplying a cleaning fluid to a surface to be cleaned, the air/liquid separation system comprising: a recovery tank assembly including a recovery tank defining a tank chamber with a top opening, the recovery tank including a bottom wall, a curvilinear exterior side wall extending upward from the bottom wall to the top opening, and a relatively planar interior side wall extending upward from the bottom wall to the top opening and connected to the curvilinear exterior side wall, the relatively planar interior side wall and the curvilinear exterior side wall together surround the tank chamber and define the top opening, wherein the bottom wall has an inlet opening and an outlet opening, the inlet opening receives said working air stream; an inlet stack for receiving said working air stream with extracted liquid and debris entrained therein; an outlet stack for expelling air separated from said working air stream, wherein the inlet stack extends upward from the inlet opening and the outlet stack extends upward from the outlet opening; a lid assembly that defines a lid chamber having a first lid chamber opening in selective fluid communication with the tank chamber and serving as a tank chamber air outlet and a second lid chamber opening at an inlet of the outlet stack, wherein an outer perimeter of the lid assembly follows and seals to the curvilinear exterior side wall and to the relatively planar interior side wall at a top of the recovery tank to enclose the top opening of the recovery tank; wherein the lid assembly includes a downwardly-extending wall bordering at least a portion of the relatively planar interior side wall and at least a portion of the curvilinear exterior side wall and defines an open bottom cavity within the tank chamber and above an outlet of the inlet stack, and wherein a lower surface of the lid assembly at the open bottom cavity inclines upward and outward from above the outlet of the inlet stack to the downwardly-extending wall at the curvilinear exterior side wall to deflect fluid and dirt entrained in said working air stream away from the outlet of the inlet stack; and a float disposed within the tank chamber and operatively attached to and vertically translatable relative to the lid assembly to close the first lid chamber opening when liquid in the tank chamber reaches a predetermined level, wherein the float is disposed adjacent to the curvilinear exterior side wall, and the inlet stack and outlet stack are disposed transversely side-by-side in the tank chamber with the outlet stack between the float and the inlet stack. a recovery tank assembly including a recovery tank defining a tank chamber with a top opening, the recovery tank including a bottom wall, a curvilinear exterior side wall extending upward from the bottom wall to the top opening, and a relatively planar interior side wall extending upward from the bottom wall to the top opening and connected to the curvilinear exterior side wall, the relatively planar interior side wall and the curvilinear exterior side wall together surround the tank chamber and define the top opening, wherein the bottom wall has an inlet opening and an outlet opening, the inlet opening receives said working air stream; an inlet stack for receiving said working air stream with extracted liquid and debris entrained therein; an outlet stack for expelling air separated from said working air stream, wherein the inlet stack extends upward from the inlet opening and the outlet stack extends upward from the outlet opening; a lid assembly that defines a lid chamber having a first lid chamber opening in selective fluid communication with the tank chamber and serving as a tank chamber air outlet and a second lid chamber opening at an inlet of the outlet stack, wherein an outer perimeter of the lid assembly follows and seals to the curvilinear exterior side wall and to the relatively planar interior side wall at a top of the recovery tank to enclose the top opening of the recovery tank; wherein the lid assembly includes a downwardly-extending wall bordering at least a portion of the relatively planar interior side wall and at least a portion of the curvilinear exterior side wall and defines an open bottom cavity within the tank chamber and above an outlet of the inlet stack, and wherein a lower surface of the lid assembly at the open bottom cavity inclines upward and outward from above the outlet of the inlet stack to the downwardly-extending wall at the curvilinear exterior side wall to deflect fluid and dirt entrained in said working air stream away from the outlet of the inlet stack; and a float disposed within the tank chamber and operatively attached to and vertically translatable relative to the lid assembly to close the first lid chamber opening when liquid in the tank chamber reaches a predetermined level, wherein the float is disposed adjacent to the curvilinear exterior side wall, and the inlet stack and outlet stack are disposed transversely side-by-side in the tank chamber with the outlet stack between the float and the inlet stack.