An apparatus for treating a tissue site comprising a negative-pressure source configured to be fluidly coupled to the tissue site; an instillation source configured to be fluidly coupled to the tissue site; and a controller operatively coupled to the negative-pressure source and to the instillation source. The controller can be configured to operate the negative-pressure source and the instillation source to intermittently deliver negative pressure to the tissue site for a negative-pressure interval and deliver instillation fluid to the tissue site for an instillation interval. A purge volume of instillation fluid may be delivered to the tissue site at a purge frequency. In some examples, the purge volume may be delivered through the second fluid conductor and removed through the first fluid conductor during a negative-pressure interval.