Got use those high pressure waterjet with nozzles that go into the piping or not?

Sometimes its just the P elbow/junction stuck there. To access it u need the mgmt ppl to call/email the owner below and let ur plumber access the elbow from there by opening its cap and unclogged it.

Update:

The management team has found the problem to be the clogged pipe which requires us to fix it at the unit below. Now we are trying to arrange to fix it.

Never knew staying in high-rise will have this problem