Signs you have a blocked drain

How do I know a drain is blocked before it overflows?

Blockages rarely appear without warning. Common early signs:

Water draining slowly from a sink, bath or shower
Gurgling sounds from plugholes or the toilet when water drains
Unpleasant smells rising from drains or plugholes
Water rising in the toilet bowl, or the level dropping oddly
More than one appliance draining slowly at the same time
Water pooling around an outside drain or gully

A single slow sink usually means a local blockage near that fixture. When several appliances are affected at once, or an outside drain overflows, the blockage is likely in the main drain that serves the whole property. That is the more urgent situation, because wastewater can back up into the house.