The Byzantines would use a system of tubes and siphons to create a type of flamethrower capable of shooting a flammable liquid chemical at their enemies.
In this case, to rinse off means to put the water on me so that the soap (that solid or liquid substance that you use to clean something) goes off of my body.
No violence accompanied this change; the matter thrown out was in vast quantities, and the liquid material oozing out from the abysses of the earth slowly spread in extensive plains or in hillocky masses.