A woman in Casula rang me about a kitchen sink that had been full of grey water since Friday. It was Monday. On the bench sat three empty bottles: a caustic gel, an enzyme powder and a box of bicarb soda. Under the sink, the bottle trap had a bulge that was new. The blockage was a lump of fat and rice 400 mm past the trap. The chemicals never reached it. They'd sat in the trap all weekend, cooking the plastic.
So, do drain unblockers work? As a South West Sydney plumber who has opened a lot of traps, my honest answer is: sometimes, on the right blockage, in the right pipe. Most of the time they don't, and the failures cost more than the bottle. Here is what each type does to a blockage and to your pipes, and what I'd use instead. If you would rather hand it to a licensed blocked drains plumber, no call-out fee, ring 0455 222 292 and Paul answers.
Caustic drain unblockers can soften a fresh grease film in a straight, clear run of pipe, but they do little to hair, nothing to tree roots or anything past the trap, and the heat they make damages PVC and old galvanised pipe. Enzyme products are slow and only good for maintenance. Bicarb and vinegar mostly makes bubbles. For a real blockage, a plunger and a plastic drain snake beat all three.
The short version: which drain cleaner does what
| Product type | What's in it | What it actually does | Where it can help | Risk |
|---|---|---|---|---|
| Caustic gel, liquid or crystals | Sodium hydroxide, sometimes with aluminium granules | Turns fat into soap, slowly breaks down hair, makes heat | Fresh grease film in a straight run of new pipe | Heat softens PVC, strips galvanised, burns whoever opens the trap |
| Enzyme or bacterial pellets | Cultured bacteria and enzymes | Digests fat and food film over days and weeks | Monthly maintenance, septic systems | None, but no use on a full blockage |
| Bicarb soda and vinegar | A weak alkali and a weak acid | Fizzes, loosens a little surface film | A smelly, slow basin | None, and next to no effect |
What a drain unblocker actually does to a blockage
The caustic products, and that includes Drano (yes, it is sold in Australia), Diggers caustic soda, the supermarket crystals and most of the gels, are built on sodium hydroxide. It turns fat into soap, which is why it has some effect on a greasy kitchen trap, and it slowly breaks down the protein in hair. It also does something the label skips over: it gets hot. The crystal products add aluminium granules that react with the caustic to make hydrogen gas and more heat again, so the fat softens and the chemical can get at it.
Here's the catch. A caustic drain cleaner only works on what it touches. Pour it into a sink that's already full and it dilutes into ten litres of standing water and floats on top of the plug. A packed wad of hair goes slimy on the outside and stays put. If the blockage is 400 mm down the branch, in the main line or in the toilet, the chemical never gets near it, and the fine print admits as much: slow drains, not blocked drains. On a sluggish sink with a straight run of new PVC, a caustic product will sometimes buy you a few weeks. That's the best case, and the only case.
What caustic soda does to PVC, earthenware and galvanised pipe
PVC handles sodium hydroxide fine at room temperature. It doesn't handle heat. When a caustic soda drain cleaner sits on a plug and keeps reacting in one spot, the trap can get hot enough to soften and distort: the bulge I found in Casula. Old galvanised steel, still common in kitchens and laundries around Cabramatta and Fairfield, is worse: caustic attacks zinc, and zinc is the galvanising. Strip that and the bare steel underneath, already thin from 50 years of rust, goes from partly blocked to leaking. Earthenware, the glazed clay sewer pipe under most pre-1980s houses, shrugs the chemical off, but a blockage in earthenware is nearly always tree roots, and nothing on a shelf touches a root.
Enzyme drain cleaners: slow, safe and not for emergencies
An enzyme drain cleaner is a different idea. Products like Actizyme are pellets full of cultured bacteria and the enzymes they produce. You dose the drain last thing at night and the bacteria eat the film of fat and food on the pipe wall over days. Even the manufacturer says to expect some improvement in 24 hours, weeks for a badly blocked drain, and that hair usually needs pulling out by hand. There's no heat, no fumes and nothing to burn a plumber. But they won't clear a full blockage in the time you need, and a dose of caustic or bleach kills the bacteria you just paid for. Monthly on a greasy kitchen line or a septic, they earn their keep. Poured into a full sink, they're a bottle of hope.
Bicarb soda and vinegar: the fizz that fools everyone
Bicarb and vinegar is a weak alkali and a weak acid. Mix them and they cancel each other out, giving off carbon dioxide, water and a bit of salt. The fizz is the reaction using itself up, not attacking the blockage. It will freshen a smelly basin and never hurt a pipe, but it will not shift a plug of hair or a set lump of fat. Hot tap water and dishwashing liquid does more for a greasy trap, and a plunger beats both.
When the drain unblocker isn't working
Two bottles in and the water is still there. Stop. Every extra dose is more chemical in the trap for whoever opens it next, usually me. Undissolved caustic splashing out of a trap at face height is a chemical burn, which is why I ask what's gone down before I touch anything. Tell your plumber the truth. Don't chase one product with bleach, vinegar or another brand, because mixing them in a closed pipe makes fumes, and don't plunge straight after chemicals: leave it overnight, flush with cold water, then plunge. If any gets on skin or in an eye, rinse with running water and ring the NSW Poisons Information Centre on 13 11 26, any hour.
Then work out why it failed. One slow fixture means the blockage is in that trap or branch, and a plunger or snake will reach it. Two or more slow drains, a gurgling toilet, or water in the overflow relief gully outside means the main line, usually tree roots, and that's a job for the jet blaster and camera.
How to unclog a drain safely without chemicals
The best drain unblocker I own cost a few dollars. It's a plastic drain snake, the flat barbed strip from the hardware store, and it clears more drains than every bottle on the shelf combined. Here's the order I'd work in:
- Bail the water down, then plunge. Cover a basin's overflow, and block the second bowl of a double sink with a wet rag, or you're just moving air.
- Open the trap: bucket underneath, unscrew by hand, tip out, rinse, refit. Under a kitchen sink this is where the fat lives. Under a shower, lift the grate and hook the hair out with the snake.
- Feed the snake down the branch past the trap, twist, pull back slowly, repeat until it comes up clean.
- Flush with hot tap water for a minute. Not boiling water into plastic pipe, and never after chemicals.
- Still blocked, or blocked again within a week? It's further down than you can reach. Stop there.
There are step-by-step guides for a blocked shower drain and a blocked kitchen sink. A blocked toilet is the one drain no chemical should ever go into: caustic in a bowl of water does nothing to the blockage and plenty to whoever plunges it next. A cracked trap or a failed pop-up waste is a fixture repair, not a drain job.
What it costs when the bottle doesn't work
If it comes to a plumber, the Sydney 2026 price guides put a blocked drain clear at $180 to $450, with a call-out fee of $69 to $170 on top. A CCTV camera inspection is quoted on inspection and usually bundled with the clear. What moves the price is access, how far down the blockage sits, and the time of day. A sink that's slow but still draining can wait until Monday; the rate is the same with us either way. Sewage backing up through a floor waste can't.
When to call a plumber
Ring me when the plunger and the snake haven't cleared it, when the same drain blocks every few weeks, when more than one fixture is slow, or when the gully outside is wet. Ring straight away if anything is coming up that should be going down. If chemicals have already gone down, say so when you book. Clearing a drain properly means finding out why it blocked, not punching a hole through the plug. Done right. Done once.
Monarch Civil & Plumbing clears blocked drains across South West Sydney and the Macarthur region, with a 24/7 emergency line for the ones that can't wait. If you need a plumber in Casula or a plumber in Green Valley, ring 0455 222 292 and you'll get a price before the work starts.
Related guides: blocked sink and blocked drain causes and fixes.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a blocked drains plumber, no call-out fee, across Liverpool, Fairfield, Campbelltown and Camden, and the rate is the same after hours.
Blocked drain in Liverpool, Fairfield or Campbelltown?
The local pages say what is usually wrong in your suburb and what Paul does about it: blocked drains Liverpool, blocked drains Fairfield and blocked drains Campbelltown. Everywhere else within about 20 km of Austral, the blocked drains page covers how a job runs and service areas lists every suburb. No call-out fee anywhere, and the camera goes down before anything is quoted.
Frequently asked
Why is my drain unblocker not working?
Because it can't reach the blockage or can't dissolve it. Caustic products only act on what they touch, so poured into a full sink they dilute and float on top of the plug. They do very little to a packed wad of hair, nothing to tree roots, and nothing at all to a blockage in the main line or the toilet. If two doses haven't moved it, stop adding chemical, leave it overnight, flush with cold water and plunge, or open the trap.
Is caustic soda drain cleaner safe for PVC pipes?
At room temperature, yes. The problem is the heat it makes while it reacts. In a clear pipe the heat washes through. In a blocked pipe it sits in one place, and a trap or a solvent-welded joint can soften and distort. On old galvanised steel it strips the zinc coating and speeds up rust. I have replaced traps that were sound until a couple of bottles went through them.
Do enzyme drain cleaners actually work?
For maintenance, yes. Bacterial and enzyme products digest the film of fat and food on the pipe wall over days and weeks, and a monthly overnight dose keeps a greasy kitchen line or a septic system running. They will not clear a fully blocked drain in a hurry, they do little to hair, and a dose of caustic or bleach kills the bacteria. Think of them as prevention rather than rescue.
Does bicarb soda and vinegar unblock a drain?
Not really. Bicarb is a weak alkali and vinegar a weak acid, and when they meet they neutralise each other, making carbon dioxide, water and a little salt. The fizz is the reaction burning itself out, not eating the blockage. It can freshen a smelly basin and lift a little surface film, and it will never damage a pipe, but a plunger or a plastic drain snake does far more.
Can you buy Drano in Australia, and is it any good?
Yes. The American Drano brand is sold in Australia under its own name, mostly as gels, and it is a caustic product like the rest, strongly alkaline with a bleaching agent in it. It behaves the same way: some effect on a fresh grease film in a clear run of pipe, little effect on hair, none on anything past the trap, and the same heat and splash risks. The brand on the bottle matters far less than what the blockage is made of.
What is the best drain unblocker for hair?
A plastic drain snake, the barbed strip sold at hardware stores for a few dollars. Hair wraps around the trap and grate fixings, and no product dissolves it without attacking the pipe as well. Lift the grate, feed the snake in, twist and pull back slowly until it comes up clean, then run hot tap water for a minute. If the same shower blocks every few weeks, something below is catching the hair and that needs a look.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul