Why is it that when you flush the toilet, sewage comes out of the floor drain next to it?

This is a clogged drain, the water from the toilet can not be discharged in time, back to the floor drain. You can get someone to pass the drain and it will be fine.

Open the toilet tank and see what level the scoop is at when the tank is full. If the tank is full and the water is still coming in, then it must be leaking out. Use water to pull the scoop's jam up and down, the scoop's sensitivity, if there is not smooth, or difficult to move, then it is also declared that the scoop of this device is faulty, remember to press the scoop's position a little bit, don't be too high.

Expanded:

The following is the working principle of the flush toilet:

Using the drain knob and the water plug to control the water discharge and storage, when in use, rotate the drain knob, use the metal rope connecting the water plug or nylon rope to pull up the water plug, the water plug upward to pull out the outlet pipe port, the outlet pipe will be the water into the commode using the gravitational force of the water and the kinetic energy converted into the potential energy of the excretory filth will be flushed into the downpipes, and at the same time, as the water level drops to a certain level, due to the water level, the water level will be reduced to a certain level, and the water level will be reduced to a certain level. At the same time, as the water level drops to a certain level, due to the negative pressure generated by the gravity of the water will be the water plug re-pressure into the port of the outlet pipe, blocking the outlet, the water will no longer be released at this time and start a new stage of water storage.

Water level drops to flush the toilet at the same time, the float with the lever due to the water level drops due to the gravity of the float to drive the lever that opens the replenishment organ began to synchronize the replenishment; replenishment stage using the buoyancy of the float and the lever to control the replenishment of the tank, the float drops to the lowest position just when the water plug is pressed by the negative pressure into the outflow pipe port, the tank began to store water.

Reference:

Baidu Encyclopedia- Flush Toilet