(1)    Property that is excluded from a town sanitary district under s. 60.725 (1), 1995 stats., or, subject to sub. (2), property that is excluded from a town sanitary district under s. 60.725 (2), 1995 stats., shall be included in the town sanitary district, retroactive to April 19, 1990, and shall be subject to all property taxes, special assessments, special charges or other charges imposed or assessed by the town sanitary district on or after April 19, 1990.

   (2)   If a property owner installed on his or her property a private on-site wastewater treatment system that conforms with the state plumbing code, before a town sanitary district that encompasses that property came into existence, that property shall be included in the town sanitary district. If the private on-site wastewater treatment system was installed on or after 10 years before May 14, 1992, and if the property owner provides the town sanitary district with any information about the cost of the private on-site wastewater treatment system required by the district, the town sanitary district, when the district issues any assessment or charges or imposes property taxes to construct a sewage service system, shall pay or credit the property owner an amount equal to 10 percent of the cost of the private on-site wastewater treatment system, less any grants or aids received by the property owner for construction of the private on-site wastewater treatment system, multiplied by the number of years of remaining life of the private on-site wastewater treatment system. The number of years of remaining life of the private on-site wastewater treatment system is equal to 10 minus the number of years that the private on-site wastewater treatment system has been in operation.