Bubble wash is a method of final washing of home-made biodiesel through air agitation. Biodiesel floats above a quantity of water. Bubbles from an aquarium air pump and air stone are injected into the water causing the bubbles to rise. At the water/biodiesel interface, the air bubbles carry water up through the biodiesel by surface tension. Diffusion causes water soluable impurities in the biodiesel to be extracted into the water. As the bubble reaches the surface and breaks, the water is freed and percolates back down through the biodiesel again.