How to dispose of paint thinner

What is in paint thinner?

Most cans sold as paint thinner are mineral spirits. Klean-Strip Paint Thinner, for example, is 80 to 100 percent Stoddard solvent (a type of mineral spirits) plus 3 to 7 percent trimethylbenzene, according to its safety data sheet. The sheet calls it a flammable liquid with a flash point above 100°F. It also warns that it is harmful if inhaled and may be fatal if swallowed and it gets into the lungs.

Other products also get called thinner. Lacquer thinner, acetone and turpentine are different chemicals with different fire risks. Read the front label, then look up the safety data sheet (SDS) on the maker's website. Section 13 of every SDS covers disposal, and for these products it says the same thing: follow local, state and federal rules. That means your local hazardous waste program.

Your options, from best to last resort

How to reuse paint thinner after cleaning brushes

Paint solids are heavier than thinner. Give them time and they sink, leaving clear thinner on top. Both the New York State DEC and Pennsylvania DEP tell homeowners to reuse thinner this way.

1. Pour the dirty thinner into a metal can or safety can with a tight lid. New York suggests UL-approved metal safety cans, which hardware stores sell. Don't use a food or drink container.
2. Label it "used paint thinner" and write the date.
3. Close it tightly and leave it alone somewhere cool, away from pilot lights, heaters and kids. The more thinner you have, the longer it takes. New York says large amounts can take several months.
4. Slowly pour the clear thinner off the top into a second labeled can. Stop when you reach the sludge.
5. If it won't clear, pour it through a coffee filter. New York DEC suggests this to pull out paint solids.
6. Use the clean thinner for your next brush cleaning. Keep the sludge for the next step.

What to do with the sludge

The sludge at the bottom is mostly paint mixed with a little thinner. New York DEC says to dry it outdoors and put it in the household trash. Pennsylvania DEP says to mix in cat litter, sawdust or shredded newspaper and let it dry completely before it goes in the trash.

Some states are stricter. California law bans hazardous waste, including paint and solvents, from the trash. Rhode Island law also bans household hazardous waste from the regular trash. In those states, or if you're not sure, take the sludge to a hazardous waste site in a closed, labeled can.

If the paint you cleaned off came from a home built before 1978, it may contain lead. EPA says about three-quarters of U.S. homes built before 1978 still have some lead paint. Take that sludge to a hazardous waste site instead of drying it at home.

Where to take leftover thinner

Thinner goes to your city or county household hazardous waste program. That may be a full-time drop-off site or a few collection days a year. EPA suggests searching for household hazardous waste plus your zip code, or calling your local solid waste agency.

PaintCare drop-off sites, including paint stores, are a different program. PaintCare's product list says it does not take paint thinners, mineral spirits or solvents. This holds true in every PaintCare state. A hazardous waste site that is also a PaintCare site may still take thinner through its own program, so check its own list.

Two examples of how local programs work: D.C. Public Works collection events take thinners and mineral spirits for free. You must register ahead and bring proof you live in D.C. In Providence, R.I., the free Eco-Depot events take paint thinners and strippers by appointment.

Paint Again picks up paint, not thinner or other solvents. If you have both, bring the thinner to a hazardous waste site and use the pickup for the paint.

Why not the drain, the trash or letting it evaporate?

• Drains and toilets: EPA warns that hazardous products poured down drains can damage septic tanks and wastewater treatment systems. Thinner also doesn't mix with water.
• Storm drains and the ground: Pennsylvania DEP says these products should never be dumped into storm sewers, drains or onto the ground.
• The trash: liquid thinner is flammable and can leak in a garbage truck. California's CalRecycle lists paint thinners by name among wastes banned from the trash.
• Evaporating a can of it: the vapors are harmful to breathe and can catch fire. New York only allows drying very small amounts, under one cup, mixed with cat litter outdoors. Even that is not allowed in states that ban hazardous waste from the trash.

Rules by state

How to store and carry thinner safely

• Keep it in the original can with the label on. EPA says never move hazardous products into food containers.
• Store it away from heat, sparks, furnaces and pilot lights. The SDS says to keep the container tightly closed in a cool, dry place.
• Keep it away from kids and pets. Mineral spirits can be fatal if swallowed and they get into the lungs.
• If a can is rusted or leaking, set it inside a bigger leak-proof container and label it, as New York DEC advises.
• In the car, wedge cans upright in a box in the trunk or truck bed. Keep a window cracked and drive straight to the drop-off.

Unusual situations

• No label or an unknown jar: don't open it to sniff it, and don't mix it with anything. Write "unknown, possibly solvent" on it and tell the hazardous waste staff.
• Thinner mixed with other liquids: keep it separate from leftover paint and other chemicals. Mixing makes it harder to handle and can be unsafe.
• Rags and paper towels: rags soaked with oil paint, stain or linseed oil can catch fire on their own as they dry. See our oily rags guide before you toss them.
• Empty thinner cans: the SDS says empty containers still hold residue, so follow the label warnings even when empty. Ask your local program whether a fully empty, dry can goes in trash or recycling.
• Businesses and painting crews: the household rules don't cover you. A business making 100 kilograms (about 220 pounds) or less of hazardous waste a month is a very small business under EPA rules. Some counties run separate, often paid, drop-offs for these businesses. Ask yours, or hire a hazardous waste hauler.