The Property Law stipulates that who is responsible for the leakage of some upstairs drainage pipes downstairs?

There will be no such provision in the property law.

Generally speaking, according to the principle of user responsibility, the upstairs owner should be responsible unless there is evidence that the downstairs residents have caused damage to the water pipes.

During the warranty period, you can claim compensation from the developer for the losses caused by the damage of the water pipe itself. After the warranty period, the developer is no longer responsible.