What Is an Overflow Relief Gully?

It’s your sewer’s pressure-relief valve: a deliberately weak point, outside, so that when the line blocks, sewage surfaces in the garden rather than in your bathroom.

Why It Matters

• It’s designed to overflow. The gully sits lower than your indoor fixtures, with a loose grate that lifts under pressure, so sewage escapes there first, sparing the inside of your home.
• Discharge from the gully = blocked sewer. It’s one of the most unambiguous blocked-drain signs there is, and it means the blockage needs urgent attention.
• It must stay clear. A gully buried under paving, pot plants or garden beds can’t do its job, and the overflow then finds your floor wastes instead.

Where It Is

Look for a grated drain near an outside tap, laundry or bathroom wall, usually at ground level below the level of indoor drains. Like the boundary trap, it’s worth locating before you ever need it.

Common Mistakes or Misunderstandings

• “Sewage came out of a drain in the yard, but it stopped: crisis over.” It relieved the pressure; the blockage is still in the line, and it will happen again with interest.
• “I’ll seal that grate so nothing can come out.” Sealing or covering the ORG removes your home’s protection, so the next blockage overflows inside.
• “It’s a stormwater drain.” No, the ORG is on your sewer. Rainwater shouldn’t be directed into it (that overloads the sewer and is non-compliant).

When to Call a Plumber

Any sewage discharge at the gully, even once, even briefly. That’s your line telling you it’s blocked, in the politest way it knows.