Solve the problem of 12 suites, 3 second floors, only one second floor toilet backflow every time

If it is an old house and confirm that there is nothing inside the dagzag, it is recommended to check it from the following aspects:

Whether there is water accumulation in the long transverse pipes. For example, the horizontal pipe to the septic tank is lower than the septic tank level. In this case, every time you go into the water, you need to push the water in the pipe laterally, and when the water head upstairs is very urgent, you can't push it too late, and the water below will be flooded.

At the same time, the water in the transverse pipe is easy to form a soft blockage - the liquid in the pipe is in a gelatinous state, which looks like nothing, but the fluidity is poor;

Whether the septic tank is holding air. The normal sewer direction should be breathable, and the water in the building will not be discharged if the sewer is not smooth and the septic tank is holding air;

The pipes from the riser to the roof in the building must be unobstructed.

One of the drawbacks of old-fashioned sewers (both in terms of design and materials) is that when a sudden large amount of water descends, the pipes are filled, and a mass of water moves like a big piston, pressing in front and pumping in the back. So you can't simply look at it as "water flow".