Why sinks clog and what you can fix yourself

Where the clog usually starts

In a kitchen sink, the main culprit is grease. Warm dishwater carries grease into the pipe, where it cools and sticks to the pipe wall. Coffee grounds, food scraps and detergent residue then cling to it until the opening keeps narrowing.

In a bathroom sink, hair, soap scum and toothpaste dominate. They form a soft plug inside the trap that lets water through slowly, but no longer freely.

• water drains slowly but still drains — sediment has already formed
• water rises during use — the clog is further from the trap
• smell coming from the drain — sediment is fermenting on the pipe wall

What you can safely try yourself

The most effective home step is taking apart and cleaning the trap. Put a bowl or bucket under the sink, unscrew the trap by hand, remove the sediment and rinse the parts. Most minor clogs are solved right here.

A plunger works when the overflow opening is covered — otherwise the pressure escapes past it. It's not worth pouring very hot water into cast-iron pipework followed by chemicals one after another.

When it makes sense to call a professional

If the trap is clean and the water still doesn't move, the clog is deeper in the pipework. The same applies when water rises in several fixtures at once, or at a neighbour's place — that points to a shared drop pipe or stack that can't be cleared from inside the flat.

In that case a drain snake or pressure flushing is used, and if needed the pipe is inspected with a camera to see whether the cause is sediment, an incorrect slope, or a damaged pipe.

The kitchen and bathroom need different approaches

In the kitchen the sediment is greasy and sticks to the pipe wall as an even layer. Removing it needs heat and mechanical action along the whole section, not just at the trap. In the bathroom the plug is more localised: hair and soap scum gather at the trap and floor drain, where they can be removed by hand.

That's why the same approach doesn't give the same result in both rooms. In the kitchen the clog typically recurs within three to twelve months if the pipe walls are left unclean, while in the bathroom it recurs when the floor drain goes without maintenance for a long time.

What we check on site

We start by finding where the water is standing and which fixtures are affected. A problem in a single fixture points to a section inside the flat; with several fixtures we move towards the connecting pipe and the stack. If needed, we open an inspection hatch to see how the water actually moves.

If the clog is recurring, it makes sense to inspect the pipe with a camera after opening it. This reveals whether the cause is only sediment or rather an incorrect slope, a sunken section, or a damaged pipe, in which case the next clog is only a matter of time.

How to prevent a clog in advance

• pour a greasy pan's residue into paper before washing, not into the sink
• use a drain strainer and clean it regularly
• flush the drain once a week with plenty of hot water
• clean the trap and floor drain a couple of times a year