A drainage device for a tank of an aircraft, comprising a drainage duct, a drainage valve positioned between the upstream and downstream ends of the drainage duct, a housing dimensioned to house at least the downstream end of the drainage duct and a hatch moveable between an open position and a closed position in which the hatch closes the housing. The hatch comprises a liquid store positioned on the inner face thereof, into which the drainage duct opens when the hatch is in the closed position. The liquid store collects and stores liquid coming out of the drainage duct in the event of leakage from the drainage valve. Also an aircraft with such a drainage device.