Paint thinner is considered hazardous waste and must be disposed of in a manner that is safe for the environment and human health. It is basically a solvent that thins oil-based paint to the desired consistency so it can be applied easily and cleaned up. In many cases, after a painting project is done, you find you have leftover paint thinner, and you may be unsure of the correct methods of disposal.
Never Dispose of Unused Paint Thinner like Ordinary Trash
Most cities have special methods of disposal for hazardous waste. If your area does not have a hazardous waste program, you must contact the local authorities for any information on the preferred method for disposal.
Never pour unused paint thinner down drains or in the regular trash. If it ends up in landfills or the water system, it will leech into our waterways, causing harm to the marine animals and polluting our water supply.
Tip: Check with your local automotive repair and service shop or gas station. They have a tank for dirty, used oil and automotive fluids and are actually paid when a reclamation company picks it up to refine into usable oil. Most would welcome the paint thinner, as it would help fill their reservoir more quickly. That is how I get rid of all my used paint thinner safely.
Purchase Only the Required Amount
If you rarely use paint thinner, never buy large quantities you will not be using. Instead, purchase small amounts only when required. Also, try to use up all the paint thinner you have for a given project by applying additional coats of paint or by painting some small objects that need retouching. If you have still have some unused material remaining, you can give it to a friend or neighbor who plans to undertake a painting project.
Reuse Excess Paint Thinner
You can store used paint thinner and reuse it in your next painting project if you do end up having a lot left over. Wear gloves to protect your hands, and pour the used paint thinner in a glass bottle or container, closing the lid tightly. To prevent someone else from mistaking the paint thinner for something else, label it appropriately. After a few months, the paint particles will settle to the bottom leaving clear thinner on the top.
You can pour out this liquid and use it in your next painting project. Avoid pouring the paint thinner into a container that was previously used to hold edible substances, as this may interfere with the integrity of the chemical.
Dispose of the Paint Sludge
After you recover the clear paint thinner, you will be left with some colored sludge in the bottom of the container. This sludge must be disposed of in accordance with the hazardous waste disposal guidelines in your area. Call the disposal helpline and arrange for drop-off or pickup of the waste matter. If you do not have arrangements for hazardous waste disposal in your area, you can leave the sludge open in a well-ventilated area.
It will dry completely after some time, and then you can dispose of the dry remnant in the garbage can. You must, however, contact your local authorities and ensure that this is acceptable. You could also try and accelerate the drying process by adding sand or cat litter to the sludge. Dry waste is easier and environmentally better to dispose of than wet waste.
Edward Kimble, a professional painter and the author of Interior House Painting Blog, contributed to this article.