I step into the clay pit, stir it a bit, then sit down and tie a rope around my genitals that goes through a ring at the bottom of the clay pit and back up to an overhead point that is out of reach. The rope holds me down in the clay while I struggle to work myself under. I can tighten the rope attached to my crotch, but I cannot loosen it. When the rope is released from where it is anchored overhead, I am able to work my genitals back to the surface. Once there, I lie back and masturbate myself to orgasm.
Link on C4S (coming to UMD soon!): Balls Deep in the Clay