This lavoir is at Lubersac, NOT AT ST SERNIN, in the commune of Saint Sernin de Duras. As you leave the Eastern edge of the village of Lubersac, it is on the right side, as the road starts to descend. It almost looks like private land.
The lavoir is sign posted in the village of Lévignac de Guyenne but it is still not easy to find. Follow the sign near the post office then take a rough farm track down to a small irrigation lake. The lavoir is alongside the lake.