Disposing of leftover borer treatment
The end of a DIY job leaves a half-full sprayer and some empty bottles. Where they go matters, because borer insecticides are hard on waterways.
Facts and prices checked 5 November 2026
Leftover borer treatment should never go down a sink, toilet, gutter or stormwater drain. Permethrin, the usual active ingredient, is very toxic to fish and other aquatic life, and Auckland's stormwater runs untreated to streams, beaches and the harbour. The best disposal is not to have leftovers: mix only what you'll use (one concentrate's directions say to use diluted mix within 48 hours) and apply any small remainder to bare timber that needs it. Store unopened product locked away, and check Auckland Council's current guidance for hazardous household waste. The product safety notice covers handling.
Why can't borer treatment go down the drain?
Borer treatment can't go down the drain because its active ingredient harms aquatic life, and drains lead to water. Stormwater grates in the street and on driveways carry water straight to streams and the sea without treatment. Wastewater plants aren't designed to remove insecticides either. A rinse of a sprayer on the driveway can end up in the nearest stream after the next rain.
How do you avoid leftovers in the first place?
Avoid leftovers by measuring the job before you mix. Work out the timber surface area, allow about a litre of mixed product per 10 square metres per coat, and mix in batches. If there's some left at the end, use it on more bare timber that needs treating, such as a shed, a fence rail or the back of a bookcase, following the label. Our DIY cost guide walks through the sums.
| What's left | What to do |
|---|---|
| Small amount of mixed product | Apply it to other bare timber that needs treatment |
| Large amount of mixed product | Store sealed and labelled only if the label allows; otherwise treat as hazardous waste |
| Unopened or part-used concentrate | Keep in its original container, locked away, for next season |
| Old, unlabelled or unwanted product | Hazardous household waste; check council options |
| Empty container | Follow the label's container directions before recycling or rubbish |
How should you clean the sprayer?
Clean the sprayer (see borer treatment products for sprayer types) by rinsing it with a little water and spraying the rinse onto the bare timber you've just treated, never into a drain or onto the garden near a pond. Repeat once or twice. Wear gloves while you do it. Store the clean sprayer labelled for insecticide only, so it's never used for something else like watering plants.
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What do you do with empty containers?
Do what the label says with empty containers. Many pesticide labels say to triple-rinse the empty container, adding the rinsate to the spray mix, and not to reuse it for anything else. Check your label for its exact wording and for whether the container can go in household recycling or general rubbish. Never use an empty pesticide bottle for food or drink.
Where does unwanted product go in Auckland?
Unwanted product goes to a hazardous household waste option, not the rubbish bin. Auckland Council publishes how to get rid of unwanted and hazardous items, and options have included certain transfer stations and drop-off events. These change, so check the council's rubbish and recycling pages or call 09 301 0101 for the current place and any charges before you take it anywhere.
Keep the product in its original labelled container for the trip, upright and sealed, in the boot away from passengers.
Questions people ask
Can I pour leftover borer treatment on the garden?
No. It isn't made for soil or plants, it can reach waterways, and it can harm beneficial insects and pets. Use it on bare timber that needs it, such as shed framing, or dispose of it as hazardous waste.
How long does borer concentrate keep?
Unopened concentrate kept cool and sealed usually keeps well; check the label or ask the manufacturer for a shelf life. Mixed product is different: one manufacturer says to use it within 48 hours.
What if I spill borer treatment?
Soak it up with rags, paper or sand, keep it out of drains, wear gloves, and bag the waste for hazardous disposal. For a large spill near a waterway, call Auckland Council's 24-hour pollution hotline on 09 377 3107.
Short answers like this one feed into the Borer Wise guide to Auckland borer, which sets out every option from DIY to a professional visit.