An extraction pump of a printing device fluidically connected to a reservoir of the printing device is set to a specified rotational velocity. A pulse-width modulation (PWM) value of the extraction pump correspondingly increases until the extraction pump rotates at the specified rotational velocity. While the power of the extraction pump is monitored, a power of a supply pump of the printing device fluidically connected between the extraction pump and the reservoir is continually increased; the power of the extraction pump correspondingly decreases to maintain rotation of the extraction pump at the specified rotational velocity. Responsive to the power of the extraction pump decreasing to a characterized value for the specified rotational velocity, the power of the supply pump ceases being increased.