(a) A municipality may secure bonds issued under this subchapter by a pledge of the net revenue from sewer service provided outside the municipal boundaries.
(b) Bonds issued under this subchapter may be additionally secured by a pledge of all or part of the net revenue from sewer service provided inside the municipal boundaries.

(c) In the ordinance authorizing the issuance of bonds secured only by the net revenue from sewer service provided outside the municipal boundaries, the municipality may:
(1) specify each item of expense or portion of the item to be deducted to compute that net revenue; or
(2) prescribe another formula the governing body of the municipality considers appropriate to compute that net revenue.