In every lease, there is an implied warranty of habitability which requires the landlord to maintain the premises in a habitable condition by complying with local and state housing codes.  When there is a breach of the implied warranty of habitability, the tenant notifies the landlord as you have done and the landlord is required to respond within a reasonable time by making the necessary repairs.  When the landlord fails to respond within a reasonable time by making the necessary repairs, the tenant has the following options:  The tenant can make the repairs and deduct the cost from the rent or the tenant can move out and terminate the obligation to pay rent for the balance of the term of the lease or if the tenant stays on the premises, the tenant can withhold rent and defend against eviction.  Another alternative is to sue the landlord for breach of the implied warranty of habitability.  You can also contact the local housing code inspector, who can bring an enforcement action against the landlord for code violations to compel the landlord to clean up the mess and make the necessary repairs.  The sewage is a health and safety issue which constitutes a breach of the implied warranty of habitability.