An apparatus comprising: a flow-through printhead having a row of jetting channels configured to jet droplets of a print fluid, a supply manifold fluidly coupled to the row of jetting channels, and a return manifold fluidly coupled to the row of jetting channels; a first reservoir fluidly coupled to the supply manifold; a second reservoir fluidly coupled to the return manifold; a first pressure source at the first reservoir; a second pressure source at the second reservoir; and a controller communicatively coupled to the first pressure source and the second pressure source; wherein: the first reservoir and the second reservoir have at least either one of a feature (i) that the first reservoir and the second reservoir are fluidly isolated except through the printhead and a feature (ii) that the first reservoir and the second reservoir are mounted in-line with the row of jetting channels; the controller is configured to control the first pressure source and the second pressure source to create a first pressure differential between the first reservoir and the second reservoir to produce a flow of the print fluid between the first reservoir and the second reservoir through the printhead; the controller is configured to determine whether to reverse the flow of the print fluid, and to control the first pressure source and the second pressure source to create a second pressure differential between the first reservoir and the second reservoir to reverse the flow of the print fluid between the first reservoir and the second reservoir through the printhead; and the controller is configured to monitor a time since a last reversal of the flow of the print fluid, and to determine whether to reverse the flow of the print fluid based on the time since the last reversal of the flow of the print fluid. a flow-through printhead having a row of jetting channels configured to jet droplets of a print fluid, a supply manifold fluidly coupled to the row of jetting channels, and a return manifold fluidly coupled to the row of jetting channels; a first reservoir fluidly coupled to the supply manifold; a second reservoir fluidly coupled to the return manifold; a first pressure source at the first reservoir; a second pressure source at the second reservoir; and a controller communicatively coupled to the first pressure source and the second pressure source; wherein: the first reservoir and the second reservoir have at least either one of a feature (i) that the first reservoir and the second reservoir are fluidly isolated except through the printhead and a feature (ii) that the first reservoir and the second reservoir are mounted in-line with the row of jetting channels; the controller is configured to control the first pressure source and the second pressure source to create a first pressure differential between the first reservoir and the second reservoir to produce a flow of the print fluid between the first reservoir and the second reservoir through the printhead; the controller is configured to determine whether to reverse the flow of the print fluid, and to control the first pressure source and the second pressure source to create a second pressure differential between the first reservoir and the second reservoir to reverse the flow of the print fluid between the first reservoir and the second reservoir through the printhead; and the controller is configured to monitor a time since a last reversal of the flow of the print fluid, and to determine whether to reverse the flow of the print fluid based on the time since the last reversal of the flow of the print fluid. the first reservoir and the second reservoir have at least either one of a feature (i) that the first reservoir and the second reservoir are fluidly isolated except through the printhead and a feature (ii) that the first reservoir and the second reservoir are mounted in-line with the row of jetting channels; the controller is configured to control the first pressure source and the second pressure source to create a first pressure differential between the first reservoir and the second reservoir to produce a flow of the print fluid between the first reservoir and the second reservoir through the printhead; the controller is configured to determine whether to reverse the flow of the print fluid, and to control the first pressure source and the second pressure source to create a second pressure differential between the first reservoir and the second reservoir to reverse the flow of the print fluid between the first reservoir and the second reservoir through the printhead; and the controller is configured to monitor a time since a last reversal of the flow of the print fluid, and to determine whether to reverse the flow of the print fluid based on the time since the last reversal of the flow of the print fluid.