The sewer pipe in the cupboard downstairs is leaking, there is no water leaking above the ceiling, a

It could be that the pipes in the wall are broken.

Open the cabinet first to see if there is any obvious water leakage, if there is no water on the ground, it is mostly a problem with the pipes in the wall, either the water pipe you said is leaking in the wall, or the water pipe embedded in your decoration is leaking.

Go downstairs, remove the ceiling, see the approximate location of the leak, and then go back to your home to see the area and determine what pipe is leaking.

If the sewer pipe is damaged during civil construction, then there is a reason to negotiate with the property and ask for repairs If the buried water pipe is damaged when you renovate, it is your responsibility. If you are decorating with a renovation company, you can go to a renovation company, and the law stipulates that the shelf life of concealed works (water, electricity, waterproof) is five years.

However, it needs to be said that either way, it is definitely necessary to dig the wall and dig the ground.

It's hard to say this, because if you want to hold others accountable, you must have evidence to prove it, otherwise it's all in vain.

You've made it clear that if the drain pipe in your kitchen is leaking, how should the upstairs be responsible?

Look, this shouldn't have anything to do with upstairs! This question. If this problem is specific, you can communicate with your property, which should have something to do with the developer