A system for treating a tissue site, comprising: a dressing configured to be placed on the tissue site; an exudate container; a negative-pressure source fluidly coupled to the dressing and to the exudate container, the negative-pressure source configured for a negative-pressure interval and a venting interval; a solution source; and an instillation regulator fluidly coupled to the solution source and to the negative-pressure source, the instillation regulator configured to draw a solution from the solution source during the negative-pressure interval and to instill the solution to the dressing during the venting interval characterised in that the instillation regulator comprises: a housing coupled to the exudate container; a piston disposed in the housing and partitioning the housing into a first chamber and a second chamber; a solution inlet port fluidly coupled to the solution source and to the first chamber; a solution outlet port fluidly coupled to the dressing and to the first chamber; and a negative-pressure port fluidly coupled to the negative-pressure source and to the second chamber; wherein the piston is actuated by negative-pressure applied to the negative-pressure port during the negative-pressure interval to draw the solution into the first chamber through the solution inlet port and to instill the solution from the first chamber through the solution outlet port during the venting interval. a dressing configured to be placed on the tissue site; an exudate container; a negative-pressure source fluidly coupled to the dressing and to the exudate container, the negative-pressure source configured for a negative-pressure interval and a venting interval; a solution source; and an instillation regulator fluidly coupled to the solution source and to the negative-pressure source, the instillation regulator configured to draw a solution from the solution source during the negative-pressure interval and to instill the solution to the dressing during the venting interval characterised in that the instillation regulator comprises: a housing coupled to the exudate container; a piston disposed in the housing and partitioning the housing into a first chamber and a second chamber; a solution inlet port fluidly coupled to the solution source and to the first chamber; a solution outlet port fluidly coupled to the dressing and to the first chamber; and a negative-pressure port fluidly coupled to the negative-pressure source and to the second chamber; wherein the piston is actuated by negative-pressure applied to the negative-pressure port during the negative-pressure interval to draw the solution into the first chamber through the solution inlet port and to instill the solution from the first chamber through the solution outlet port during the venting interval. a housing coupled to the exudate container; a piston disposed in the housing and partitioning the housing into a first chamber and a second chamber; a solution inlet port fluidly coupled to the solution source and to the first chamber; a solution outlet port fluidly coupled to the dressing and to the first chamber; and a negative-pressure port fluidly coupled to the negative-pressure source and to the second chamber; wherein the piston is actuated by negative-pressure applied to the negative-pressure port during the negative-pressure interval to draw the solution into the first chamber through the solution inlet port and to instill the solution from the first chamber through the solution outlet port during the venting interval.