N.Y. Gen. Mun. Law § 120-A
The respective municipalities and districts may contract with each other, or they may jointly or severally contract with a third person, corporation or municipality, either for the construction, operation, maintenance or leasing of a complete comprehensive system for the removal and disposal of sewerage, or of a trunk line system with or without lateral connections, with or without the sewerage disposal plant or of a sewerage disposal plant; each of the boards or commissioners, however, binding only the municipalities or districts which they respectively represent. Such municipalities jointly acting through such board or commissioners, if they deem it expedient so to do, may contract with any other municipality or municipalities through or over whose territory such trunk sewer or sewers are intended to pass, for the construction of said outlet, trunk sewer or sewers and appurtenances located within the territory of such other municipality, in such manner as may be agreed upon between such other municipality, and the municipality theretofore jointly contracting as herein authorized, or such jointly contracting municipalities may contract in writing with any other municipality or municipalities for the privilege of connecting its or their sewers and drains with such outlet or trunk sewer or sewers so to be jointly constructed by the municipalities originally contracting for the public improvements or works hereby authorized, and it shall be lawful for such other municipality or municipalities to enter into a contract for such purpose, upon such terms and for such consideration and length of time as may be mutually agreed upon between all the contracting municipalities.
N.Y. Gen. Mun. Law § 120-A