Whose resposibility

I recently bought a restaurant. It is located on the 2nd floor. Several waterleakages occurred due to the clog of pipes.It caused severe damage to downstair business. The clog was caused by a ball of grace (oil). Downstairs business tenant and the landloard blame us, as it is mine respon*****ility to inspect the pipes. While my point is the clog is cause by the previous business owner, so it should be the landlord's respon*****ility to rent a clean and ready to operate building to the new tenant.
I am looking for some lawful suggestion on whose respon*****ility it is to the leaking damage. Thank you very much