Pump priming primer suction bulb iRobot Scooba 5800 5900 330 340 380 390 385 all past models. 

Tip can be trimmed if necessary to fit your Scooba's pump port. 

Is your "tank full" light coming on even when it's empty? Does it then run for a few seconds and beep?  More than likely, you need this bulb. Prime the pump when the Scooba has been dry for 30+ days.