Balls tied
Tie the string around the base of your balls. Then tie between the balls around the base, between the balls from the other direction and so forth. You should keep them tied for at least a half hour. Also tie a separate string around the base of your cock. This must all be tied tightly. Now put your pants on and go out and about. After half an hour, wank yourself off. When you finish cumming you can un tie your cock and balls. Take photos at various stages and report back!