The mitigation of fuel propellant sloshing onboard satellites or during space launches is of particular interest. Fuel sloshing can indeed significantly affect spacecraft motion by increasing the maneuver settling time and occasionally destabilizing them. This paper presents a novel, model-free attitude control approach that actively compensates for the sloshing disturbance. One of the main novelties consists of using pressure sensors inside the fuel tank to measure a quantity proportional to the sloshing torque. Then, using this measurement, an attitude controller can be designed not only to reject the sloshing torque but also to keep the fuel sloshing within acceptable conditions. Technically speaking, this is achieved by combining model-free control with an output to input saturation transformation (OIST) add-on.