One example of a system includes a bulk ink assembly, a printhead assembly, a valve, and a controller. The bulk ink assembly receives a bulk ink supply. The printhead assembly includes nozzles to eject ink drops, a collapsible container to supply ink to the nozzles, and a sensor to provide a sensor signal indicating the amount of ink within the collapsible container. The valve supplies ink to the collapsible container from the bulk ink assembly in response to a control signal. The controller provides the control signal based on the sensor signal to regulate the amount of ink in the collapsible container and to provide an out of ink signal based on the sensor signal indicating the bulk ink supply is effectively empty.