Explain that the jar of clean water is our mind. Begin by putting one rock in. This could represent seeing one inappropriate movie or TV show (watch the dirt you couldn’t see on the rock before float to the bottom). Add another rock, representing one pornographic image. More dirt floats to the bottom. Another rock: a inappropriate joke. Another rock: a cuss word or two. Another rock: one alcoholic drink or cigarette. Another rock: inappropriate music. By now the water isn’t so clear anymore and the jar is heavy. Likewise, our spirits become weighed down with sin when we participate in activities that are not Heavenly Father’s standards. Explain that through the atonement we have the opportunity to repent and be forgiven and what a blessing it is to rid ourselves of those heavy sins. Remove the rocks. Our sins can be forgiven and we can feel the freedom and joy that comes only through the atonement. Over time and with faithful obedience to the commandments we can put our sins behind us. Then either replace the jar with one filled with clean water, or simply fill the jar until with clean water until the dirty water overflows (hopefully into a cake pan or something) and only clean water remains.