A dismountable mixing device (100) for mixing at least two liquids inside a tank of a mobile machinery equipment, the mixing device includes a pump unit (10), a suction hose (12), and a return hose (14). The pump unit has an inlet port and an outlet port. The suction hose has one end connected to the inlet port of the pump unit, and a sucking end inserted into the tank through a first opening. The return hose has one end connected to the outlet port of the pump unit, and a returning end inserted into the tank through a second opening. The pump unit is driven to suck the liquids from the tank via the suction hose, and return the liquids back to the tank via the return hose.