Wis. Admin. Code NR § 811.851
Wastes from toilet facilities shall be discharged to a sanitary sewer system. The floor elevation of a building from which there is a discharge shall be constructed at least one foot above the rim of the nearest sanitary sewer manhole in accordance with s. NR 811.25 (1) (h) to prevent contamination from sewer backup. When a sanitary sewer system is not available, the department may approve the discharge to a holding tank or an individual POWTS if the installation meets ch. SPS 383 requirements and if the POWTS separation distances to a community water system well comply with the requirements under s. NR 811.12 (5) (d). A holding tank or POWTS shall meet the requirements under s. NR 811.25 (1) (h) 2. c.
Wis. Admin. Code Department of Natural Resources § NR 811.851