Safety Services


Disposal of hazardous waste via sinks

Some hazardous waste can be disposed of through dilution via designated sinks. Departmental Hazardous Waste Plans will describe what hazardous waste can be disposed of in this way and the process.

Mirror Non-hazardous (MN) and Mirror Hazardous (MH) waste that is below the threshold may be disposed of through dilution down designated sinks. Your department's Hazardous Management Plan will identify the hazardous waste that can be disposed of via designated sinks.

> Read about definitions of hazardous waste classifications

You can only use designated sinks to dispose of hazardous waste. Sinks must be linked to the effluent system. Do not use sinks that are not on the main sewage system or lead to the storm drain system. Absolute Hazardous (AH) waste must never be disposed of via the sink

To dispose of hazardous waste via designated sinks, the substance must be diluted no matter how low the original concentration of the waste. 

Departmental Hazardous Waste Management Plans will identify:

  • Hazardous substances produced by the department that can be disposed of via the sink
  • Sinks that are suitable for the disposal of hazardous waste
  • The correct PPE that should be worn for the laboratory, task and substance(s)

Precautions to take when disposing of hazardous waste via sinks

  • Run the water tap (before disposing of the substance)
  • Work slowly to avoid splashes
  • Keep the water running throughout the disposal and for 2 minutes afterward
  • The departmental Hazardous Waste Management Plan will have specific documented procedures and a list of substances. If additional precautions are needed, this should be repeated in the risk assessment for the specific task, as part of the control measures to ensure all users are aware of the additions to the generic procedure
  • Always refresh your knowledge on how to dispose of the specific substance

Hazardous substances that can be disposed of via sinks

  • Be below the threshold for MH or by proven to be non-hazardous
  • Be limited quantities – usually fewer than 100g or 100ml
  • A pH between 6 and 10 – no strong acids as plumbing tends to be plastic which reacts

Hazardous substances that should not be disposed via sinks

  • Substances that cause a risk of fire or explosion
  • Corrosive waste as plumbing tends to be plastic
  • Solid or viscous waste that will not dissolve in water or will remain at a high viscosity 
  • Waste that is heated and will retain a heat great enough to inhibit wastewater treatment even after dilution i.e. no liquid or vapour that would have a heat of 65.5C (150F) when it reaches the sewer, in most cases this means that the volume would need to be in excess of a litre while amounts less than 100ml will have sufficiently cooled when mixed or followed by cold water
  • Waste that the Water Authorities have stated will interfere with the wastewater treatment
  • Substances that are known to be hazardous to the environment
  • Substances that are known to be bioaccumulative including solutions containing heavy metals i.e. most heavy metals can bioaccumulate and if there is leak in any part of the sewage system, the environmental effect could cause unmonitored harm until the leak is discovered (if it is discovered)

Last updated: Wednesday, May 18, 2022