Recently company bought an apartment unit for foreign workers and faced the same problem as you.

At first I think not fair but then again the water flow from your unit to that particular joint and down. It is being used by you but it's also open for sabotage. For us, bangladeshi u know la... basically dump everything in until clogged and then leaking. Heavy oil usage with curry and frying. What to say... now under unit complain again and we even reroute incoming water along with outgoing. Seems like very hard to pinpoint what exactly is the problem.