DIY
How to Unblock a Drain Yourself
Find which drain is blocked, then work through hot water, plunger, trap cap, snake and rods, in that order.
DIY
Drain cleaners work on soft, organic blockages close to the plughole: hair, soap scum and grease in a sink, basin or shower that is slow but still draining. They do not clear tree roots, silt, wipes in bulk, dropped objects or a broken pipe, and in a drain that is fully blocked they sit in the standing water. For most blockages a plunger, the trap's cleaning cap or a drain snake is faster and safer. Our guide on how to unblock a drain sets out that order.
This page compares drain cleaners by type rather than by brand. Retail shelves change, but the active ingredients do not, and the ingredient is what decides what a product can clear and how it can hurt you. Check the label or the safety data sheet for the active ingredient before you buy.
There are five broad types. Caustic cleaners (sodium hydroxide) turn grease into soap and break down hair. Acid cleaners (usually sulphuric acid) are the most aggressive and the most dangerous. Oxidising cleaners use bleach or peroxide, often mixed with caustic in gels. Enzyme and bacterial cleaners digest organic film slowly. Mechanical cleaners, such as plungers, snakes and rods, physically remove the blockage.
| Type | Typical active ingredient | Works on | Does not work on | Main hazard |
|---|---|---|---|---|
| Caustic (alkaline) | Sodium hydroxide, sometimes potassium hydroxide | Grease, soap scum, hair near the plughole | Roots, silt, objects, full blockages | Severe skin and eye burns; heat |
| Acid | Sulphuric acid, sometimes hydrochloric | Hair, paper, grease, soap | Roots, silt, objects, collapsed pipe | Severe burns; violent reaction with water and other chemicals |
| Oxidising | Sodium hypochlorite (bleach), peroxides | Organic film, smells; some hair | Grease build-up, full blockages | Toxic gas if mixed with acid or ammonia |
| Enzyme / bacterial | Enzymes and bacterial cultures | Fat, soap and food film over days | Any full blockage; hair mats; roots | Low; follow the label |
| Mechanical | Plunger, hand snake, drain rods | Hair, paper, wipes, soft blockages | Roots and structural faults | Splash-back; stuck rods |
Caustic products are the most common household drain cleaners, sold as gels, liquids or granules. Sodium hydroxide reacts with fats to form soap, a process called saponification, which is why it shifts grease, and it breaks down the protein in hair. Some caustic products generate heat when they meet water. They work best on a basin or shower waste that is slow but still flowing, so the product actually reaches the clog.
Concentrated acid cleaners, usually based on sulphuric acid, are the strongest products available and are often sold as trade or professional products. They dissolve hair, paper and grease quickly. They also react violently with water, generating a lot of heat and the risk of spattering, and they release toxic chlorine gas if they meet bleach. Their safety data sheets list severe skin burns and eye damage. They are not a sensible household product.
These use sodium hypochlorite (the active ingredient in bleach) or a peroxide to break down organic matter. Some supermarket gels combine bleach with caustic. They are good at killing the smell from a basin or shower waste and can loosen a light soap and hair film, but on their own they make little impression on a solid grease or hair blockage.
Enzyme cleaners digest fat, soap and food residue rather than burning through it. They are slow, working over hours or days, and they need to reach the build-up, so they suit maintenance of a drain that still flows. They are the lowest-hazard option chemically, but they will not clear a drain that has stopped.
Strictly speaking a plunger, a plastic hair-removal strip, a hand snake or a set of drain rods is a drain cleaner too, and for most household blockages it is the best one. Mechanical tools pull the blockage out or break it up, carry no chemical risk, and tell you something useful when they fail: that the problem is further down or structural.
No drain cleaner clears tree roots, silt or soil, a dropped object, a mass of wipes or sanitary products, or a pipe that has cracked, sagged or collapsed. Nor will a cleaner poured into a sink reach fat that has built up metres away in the drain under the garden. If the blockage is any of these, a chemical just adds a hazard to the problem.
Roots need cutting and the pipe needs inspecting: see tree root removal. Fat lining a long section of pipe is removed by hydro-jetting, not by anything poured from above. And a blockage that keeps returning in the same place is almost always a pipe fault that a camera inspection will find.
Because the risks are real and the success rate on a properly blocked drain is low. Caustic and acid cleaners cause serious chemical burns and eye injuries, and splash-back from the plughole is a known way people get hurt. Some products generate heat inside the pipe. Mixing products can release toxic gas. And a cleaner that does not clear the drain leaves a pipe full of corrosive water for the next person who opens it.
Use one product, on one slow fixture, exactly as the label says. Wear rubber gloves and eye protection, ventilate the room, and keep children and pets well away. Never use a chemical on a drain that is not moving at all, never mix products or add a second one later, and never plunge or use a snake afterwards until it has been flushed through as directed.
Call the National Poisons Centre on 0800 764 766 (0800 POISON), available 24 hours. For skin, remove contaminated clothing and rinse with lots of running water. For eyes, rinse gently with running water for at least 15 minutes. If it is swallowed, rinse the mouth and do not make the person vomit. Call 111 if someone is unconscious, struggling to breathe or looks very unwell.
This first aid follows the National Poisons Centre and Health New Zealand. Health New Zealand advises calling 111 straight away if a chemical in the eye is causing burning or stinging. Have the product container with you when you call, so you can read out the ingredients. If fumes have been breathed in, move to fresh air.
Keep it in its original, labelled container and take it to a council hazardous waste drop-off. Auckland Council asks that household hazardous waste does not go in the rubbish or recycling bin, or down any drain, and several of its transfer stations and resource recovery centres accept household chemicals. Check the council's website for the nearest site and what it accepts before you go.
Do not decant leftovers into drink bottles or unlabelled containers, and do not combine two half-used products to save space. Mixing is how household chemical gas incidents happen.
The best drain cleaner is the one matched to the blockage, and for most jobs that is a tool rather than a chemical. Hair in a shower or basin comes out best with a plastic hair-removal strip or a hand snake. A slow, greasy kitchen sink responds to hot water and detergent, with an enzyme product for maintenance. Toilets need a plunger or toilet auger. Roots and outside drains need a drainlayer.
| The job | Best first choice | If that fails |
|---|---|---|
| Hair in a shower or basin | Hair-removal strip, then a hand snake | Caustic gel, per label, while it still drains |
| Slow kitchen sink (grease) | Hot tap water and dishwashing liquid; open the trap's cleaning cap | Hand snake; jetting if the line is lined with fat |
| Smelly but draining waste | Run water to refill the trap; clean the grate | Enzyme cleaner overnight |
| Toilet | Flanged plunger | Toilet auger; call if several fixtures are affected |
| Outside gully or drain | Drain rods from an inspection point | Drainlayer with a drain machine or jetter |
| Recurring blockage | Camera inspection to find the cause | Repair the pipe fault |
Our step-by-step guides cover the kitchen and bathroom sink and the blocked toilet in detail.
Mechanical clearing first. Drainlayers use plungers and hand augers on fixtures, powered drain machines with cutting heads for the main drain, and high-pressure water jetting to scour fat and silt off the pipe wall. Where a drain keeps blocking, they put a camera down it to find the cause. For maintenance between visits, enzyme products and strainers do more good than repeated chemical doses.
That is also what we would suggest at home: pull out what you can reach, use a plunger, open the trap's cleaning cap if it has one, and only then think about a chemical, on a single slow fixture. If you are past that point, our drain unblocking service clears it with the same mechanical tools, and our cost guide explains what drives the price. To stop it happening again, see what not to put down the drain.
The most aggressive products on sale are concentrated sulphuric acid cleaners, followed by high-strength caustic. Strongest is not the same as best. These products cause severe burns, can react violently with water and other chemicals, and still cannot clear roots, silt or a broken pipe. If a drain needs something that strong, it usually needs a mechanical clear instead.
No product clears a drain instantly and reliably. The closest thing to instant is mechanical: pulling hair out with a plastic strip, or a few minutes with a plunger and the overflow sealed. Caustic gels may shift a slow hair or soap clog within the contact time on the label, but only if the drain is still flowing so the gel can reach it.
Not until the product has been fully flushed through as the label directs. Plunging pushes and pulls the water in the pipe, and it can throw caustic or acid back out of the plughole onto your face, hands and the surrounding surfaces. If the cleaner has not worked, leave the plunger alone, keep people away from the fixture, and tell whoever comes to clear it what is in the drain.
No. A drain cleaner poured from a sink is diluted long before it reaches roots in the outside drain, and roots that have grown in through a joint keep growing back from outside the pipe. Roots are cleared by cutting or jetting, and the joint they entered through needs inspecting with a camera to decide whether a repair is worthwhile.
Check the label, which usually says. Strong caustic, acid and bleach products in quantity can upset the bacteria a septic tank relies on, and some labels warn against regular use. Enzyme and bacterial products are generally the option marketed as septic-safe. Our guide to looking after a septic tank covers pump-outs and inspections. Either way, use mechanical clearing first and chemicals sparingly.
Yes. Acid cleaners and bleach-based cleaners together release chlorine gas, and acid and caustic products react violently with each other, producing heat and spatter. Never pour a second product into a drain that still holds the first, and never combine leftovers in one bottle. If you breathe in fumes, get to fresh air and call the Poisons Centre on 0800 764 766.
Tell us what it is doing and we will tell you what it probably is, what it takes to fix, and what that should cost.