Floor Drains Fact Sheet
This guidance document is advisory in nature but is binding on an agency until amended by such agency. A guidance document does not include internal procedural documents that only affect the internal operations of the agency and does not impose additional requirements or penalties on regulated parties or include confidential information or rules and regulations made in accordance with the Administrative Procedure Act. If you believe that this guidance document imposes additional requirements or penalties on regulated parties, you may request a review of the document.

Form #:  12-026
Guidance Documents
Revised: 11/22/16


A floor drain in a dwelling garage may be connected to an onsite wastewater treatment system provided the drain does not receive petroleum products, paint, organic solvents, antifreeze or hazardous materials and meets the design requirements of Title 124 - Rules and Regulations for the Design, Operation, and Maintenance of Onsite Wastewater Treatment Systems. These drains are designed to handle snow and ice melt along with occasional exterior vehicle washing.

A floor drain in a dwelling garage that is connected to an onsite wastewater treatment system must meet the following design requirements:
  • The drain must have an integral mud trap and oil separator; and
  • The drain must be equipped with a watertight cap or a valve that is located immediately following the drain. The cap must normally be left secured on the drain or the valve must normally be left closed.
The design flow of the onsite wastewater treatment system must be increased at least 100 gallons to account for a dwelling garage floor drain connection to the system. A permanent sign must be placed within view of the drain stating "WARNING - Water Only! Floor Drain Leads to an Onsite Wastewater Treatment System to remind current and future owners that the garage drain leads to an onsite wastewater treatment system that cannot properly treat some types of wastes.




Title 124 prohibits the discharge of motor vehicle wastes or maintenance shop wastes to a septic system or to a soil absorption system. In addition, the connection of a floor drain from a maintenance shop to a septic system or soil absorption system is also prohibited. The discharge of a non-domestic waste to a septic system is subject to the requirements of Title 122 - Rules and Regulations for Underground Injection and Mineral Production Wells.