How do you tell if your outside drain is blocked?
The short answer
Lift the drain cover and look. If the chamber is full or standing with water, the blockage is downstream of it; if it's empty and dry while the house is backing up, the blockage is between the house and that chamber. Gurgling, bad smells outside, and several fixtures draining slowly at once all point the same way.
The single most useful diagnostic in domestic drainage is lifting the cover and looking in the chamber, because it tells you which side of that point the problem is on. Full means it can't get away past there. Empty, while your sinks are backing up, means it isn't getting that far.
The signs inside the house are worth reading as a set. One slow sink is a sink problem. The ground floor sinks, the bath and the loo all misbehaving together — gurgling when you flush, water rising in the shower when the washing machine drains — is a drain problem, and it's telling you the blockage is common to all of them.
Before you pay anyone to clear it, read the next answer in this list about shared drains. In a Macclesfield terrace there's a decent chance the blocked drain isn't legally yours at all, and that United Utilities will come and clear it for nothing.
One caution: drain covers can be heavy and the edges can be sharp. Lift with a proper key if you have one, and not one-handed.
- Full chamber = blockage further down the run
- Empty chamber but backed-up house = blockage before it
- Gurgling, smells and several slow fixtures at once
- Water rising in the shower when the washing machine drains
- Terraced house? Check whose drain it is before you pay to clear it
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