The rule that comes first: never mix
Before disposal, the safety basics. Never mix bleach with ammonia, acids, or other cleaners. The Clorox bleach safety data sheet and the National Capital Poison Center both warn that combining bleach with ammonia releases chloramine gas, and with acids (toilet-bowl cleaners, rust removers, drain cleaners) releases chlorine gas — fumes that can be strong enough to be fatal. New Mexico State University's extension guidance says the same. Keep products in their original labeled containers, and if you ever mix chemicals by accident and feel ill, call Poison Control at 1-800-222-1222.
Liquid bleach
Plain chlorine bleach is water-soluble, and small leftover amounts can generally be flushed away. NMSU Extension states that leftover bleach can be flushed down the toilet or washed down a drain followed with plenty of water, and the Clorox safety data sheet routes bleach residue to the sanitary sewer (never a storm drain, since bleach is toxic to fish), advising you flush the drain before and after.
Two caveats: this assumes your home is on a municipal sewer — if you're on a septic system, avoid pouring bleach down the drain. And for anything beyond small household amounts, the Clorox sheet says to contact your treatment facility first. Dilute with lots of running water, and never pour it where it can reach a storm drain or waterway.
Household cleaners
The test is simple: if a product is normally rinsed down the drain during use — as most water-based cleaners and detergents are — it can usually be disposed of by pouring it slowly down the drain with running water, per NMSU Extension.
The exceptions are solvent-based products. Metal polishes, wood polishes, waxes, and oven or drain cleaners containing lye (sodium hydroxide) should not go down the drain — store them for a household hazardous waste collection instead. When a label lists lye, hydroxide, or hypochlorite, or warns it's corrosive or flammable, treat it as hazardous waste.
Pool chemicals and paint thinner — hazardous waste
Pool chemicals (chlorine tablets, shock, muriatic acid, algaecide) are reactive and corrosive. The EPA warns that chlorine-based pool products must never be mixed with acids or other incompatible substances, which can generate toxic gas or fire. Don't pour them down any drain or put them in the trash — take them to a household hazardous waste facility in their original containers.
Paint thinner, mineral spirits and turpentine are likewise HHW and must never go down a drain, into a storm sewer, or in the trash as liquid. A useful tip from NY DEC: you can reuse them. Cap the container and let the paint sludge settle (or filter it through coffee filters), pour off the clear solvent to use again, then dry the leftover sludge outdoors and discard the dried residue in household trash.
Where hazardous chemicals actually go
Anything that's corrosive, flammable, reactive or toxic — solvents, pool chemicals, oven/drain cleaners with lye, pesticides — is household hazardous waste, and the destination is your local HHW program. The EPA strongly recommends never pouring these down the drain, on the ground, or into storm sewers, and directs residents to their local solid-waste district for collection options. Many HHW collection events are free for residents (Illinois EPA, for example, runs free public collections).
Keep products in their original labeled containers, never mix them, and transport them upright and sealed. Even empty HHW containers can hold hazardous residue — seal them and, unless the label says otherwise, discard with household trash (and don't reuse bleach containers).