The private drain usually runs from the house to the boundary or to the public connection. Past that point the sewer belongs to Uisce Éireann. If neighbours are affected, or water is rising in the road, contact Uisce Éireann before booking anyone.
The technician lifts the nearest chambers, checks which are full and decides whether the block is on your run or beyond it.
Note where the overflow is, how far it has spread and whether rain is making it worse.
Parts of Galway city have older combined drains carrying both rain and foul water, so a heavy shower can push a partial blockage over the top.