The signs
The signs it's the sewer line
A blocked sewer drain backs up through the lowest fixture first, usually the shower floor waste or the overflow relief gully outside. That's why the signs show up away from the tap you just ran. If only one sink or basin is slow, it's most likely a single blocked drain, not the sewer.
- The shower or floor waste fills when the toilet is flushed
- The gully outside overflows or smells of sewage
- Toilets gurgle when the washing machine empties
- More than one toilet or drain is slow at the same time

