To provide a means for not exceeding a maximum capacity in a toilet tank without mixing dissolved sludge into a sludge removing circulating device in a vacuum type toilet tank for a car connected outside the toilet tank when dissolving sludge in the toilet tank for the car and washing the inside of the toilet tank.

In the sludge removing circulating device in the vacuum type toilet tank for the car, a detergent for accelerating dissolution of sludge is injected into the toilet tank for the car. In the sludge removing circulating device for the vacuum type toilet tank for the car, a water gauge recognizing a capacity so as not to exceed the maximum capacity in the toilet tank and a filter for preventing the dissolved sludge from mixing into the circulating device are disposed, and the detergent is circulated in the toilet tank.