How to Flush Down the Drain

Source: Missouri Household Hazardous Waste Telephone Advice Manual, April 1994, Household Hazardous Waste Project

Pipes Never flush household hazardous wastes down the drain unless instructed to do so by local waste officials. If you are instructed to dispose of household hazardous wastes down the drain, this guide provides instructions on how to safely do so.

You should know that all drains do not lead to the same place. There are three main types of sewer systems: municipal sanitary sewer systems, septic tanks, and storm drains. A few municipalities have combined (sanitary and storm) sewers. Important differences exist in how wastes are treated and where they finally end up with each of these systems. It is critical that only the recommended type(s) of sewer system be used for disposing of household hazardous wastes.

Municipal Sewer Systems

In areas connected to municipal sewer systems, wastes flow into underground pipes from residences, office buildings, businesses, and schools. These pipes eventually drain into a wastewater treatment plant. The degree of treatment depends on the type of system. After treatment, the effluent is discharged into lakes, streams, or rivers. Although most waste products in the sewage are removed during treatment, some pollutants such as metals and pesticide residues may still be in the effluent when it is discharged into waterways.

Septic Tanks

In less populated areas, households often rely on an individual residence treatment system, such as a septic tank or a single family lagoon. Most often, a septic tank in combination with a drainfield serves an individual home. However, some smaller communities have constructed septic systems that serve a number of homes. In a septic system, solid materials settle out in the tank and are gradually broken down by bacteria.

The liquid sewage flows out into the drainfield where it is broken down by soil bacteria. Many hazardous chemicals can destroy the bacterial action in the septic system and drainfield. These chemicals may also pass untreated through the septic system and seep into groundwater.

Storm Drains

Storm drains are systems of ditches, culverts or underground pipes that collect storm water runoff from streets, driveways and parking lots. Usually the pipes empty the untreated water directly into lakes and rivers. When household hazardous waste is dumped down the storm drain, the waste can directly pollute surface water, groundwater, and threaten drinking water supplies. Household hazardous waste should never be dumped down storm drains.


A word of caution: The following management option may cause harm to human health and the environment if the described procedures are not followed carefully.

Gloves Goggles Materials Needed

Safety Precautions

Procedure for Flushing into a Municipal Sewer System

    If you have any doubts about whether it is safe to flush a product, call the local wastewater treatment plant.

  1. Flush the product during the working day (7:00 a.m. - 6:00 p.m.) so that it will be carried quickly through the collection system and not left in the municipal sewer system overnight.

  2. Limit the quantity of product that is flushed at one time. A general rule of thumb is 1 quart per day unless local wastewater officials specify otherwise. Flush the product down with large volumes of water (i.e. 3 flushes per quart). The toilet is often preferable to the sink but make sure you have no bowl cleaners or deodorizers in use.

  3. Pour slowly and carefully to avoid splashing.

Procedure for a Septic System If you are on a septic system or a single family lagoon, give products acceptable for flushing to someone who is connected to a municipal sewer system.


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