Liquid biohazardous waste can be decontaminated and made suitable for drain disposal in 2 ways:
Deactivate with bleach (1 part bleach to 9 parts liquid waste) for 30 minutes before pouring it down the drain.
Occasionally, liquid waste is autoclaved. Do not add bleach in this case. Read Autoclaving Guidelines for Biohazardous Waste.
For more information and for disposal instructions for solid biohazardous waste, read How to Package and Dispose of Biohazardous and Medical Waste.