I just suggested this job for the show, but felt that I ought to elaborate. THis was the first "real job" I had. I spent 2-3 months over the summer when I was 14 years old picking up trash along I-90 and I-405 in Washington State. There is nothing quite like spending 8 hours in the sun along a freeway picking up garbage. And at 14 years old, smelling like garbage for an entire summer was especially rewarding when looking at the pay (I believe that it is now $7+ per hour, but at the time it was $5).
I realize this may not be the dirtiest job that could be on the show, but for the age bracket, I believe it can take the cake.