Is it legal to let the downstairs residents repair the toilet sewer pipe that cracks, and does not a

No, the balcony is not the ceiling, it's not the upstairs problem, it's the building's problem. Either that, there is always a problem with water accumulation on the balcony.

Neighbouring rights disputes.

Article 84 of the Property Law [Principles for Handling Adjacent Relationships] The adjacent rights holders of immovable property shall correctly handle adjacent relationships in accordance with the principles of conducive to production, convenience of life, solidarity and mutual assistance, and fairness and reasonableness. >>>More

Don't easily use legal weapons, I don't know if you have negotiated with the upstairs and the property, if the upstairs is particularly unreasonable, the property is particularly irresponsible, don't sue easily as a last resort, that wastes money, wastes time, affects the mood, and the impact in the community is not good! >>>More

You didn't make it clear, did you change the toilet drain pipe, re-opened the hole in the floor slab or what? Under normal circumstances, it is the responsibility of the owner to deal with the indoor water seepage after the decoration, because the waterproof layer made by the original developer has been destroyed after the decoration, so the responsibility can only be borne by yourself; And although the property has done waterproof acceptance, it can only show that there is no problem with the waterproof treatment at that time, which does not mean that the property is responsible for your later water seepage, because it is not the property company to do the decoration for you, and there is no responsibility for the quality of the decoration of your home.

Then you need to see whether this pipe belongs to the upstairs residents or belongs to the public use pipe, if it is an individual, you must be responsible.