Customers often ask me if I recommend any particular chemical to use in a blocked drain. The short answer is generally no – a blockage is usually a physical problem and requires a physical solution.

Caustic soda and acids are often used by householders attempting to unblock blocked drains (often in conjunction with the trusty old plunger). This practice is risky because these products are highly corrosive and burn human skin quickly. If the risk yielded a good result I would say be careful and go for it but in my experience it simply doesn’t work for the reasons following.

The most common cause of drain blockages that I run into here in Adelaide is tree roots. Tree roots are very woody and you can appreciate that acid and other chemicals don’t do much to wood but let’s suppose the cause of your blocked drain happens to be a chemical that caustic soda loves to eat. Now let’s consider where this hypothetical chemical blockage is – it’s a long way down a 100mm drain (usually several metres down the drain). Every metre of 100mm drain holds about 7.85 litres of water but let’s suppose that your blockage is only 1 metre down from your toilet. How do you expect to get the caustic soda from your toilet to the blockage where it is needed? You can’t flush it down because your drain is blocked! Let’s suppose your blockage is 10m down the drain. How much caustic soda do you need to use in 78 litres of water for it to be effective even if you could get it down to the blockage? It just doesn’t work on main drains that are solidly blocked.

If you have a slow basin waste or sink waste, caustic soda might just do the trick but I only have experience with that working on one occasion that I can bring to mind. It was on a sludged sink waste which was draining slowly.

Usually a main drain blockage is a physical problem (not usually a chemical problem like a sludge that caustic soda reacts with) and requires a physical solution.