If this were not the case the heavy winter rains would wash away the soil.
Standard fruit trees must be left to take their chance; and, indeed from the lateness of their flowering, they are generally more injured by blight, and by drenching rains, which wash away the pollen of the flowers, than by the direct effects of cold.
An obvious locally-available substance would be seabird guano, which would surely wash away after the pottery was deposited in the ground.
They are useful for sexual activities in pools, showers, and other water sources because they don't wash away like water-based lubricants.
You generally only need to rinse it thoroughly with clean water to wash away dirt and grime, but can be cleaned gently with a soft sponge and mild soapy water.