A federal judge has sentenced a Waupun man to three years in prison for allegedly working on a drug-selling operation while he was in the Fond du Lac County Jail. Thirty-one-year-old Justin Kohl was serving eight months on another drug conviction at the time. Kohl chose his own replacement on the outside and stayed in touch with her on sales and collections while he was serving time. Prosecutors say the Madison-based network sold about eight pounds of meth over a three-year period. Its ringleader is serving a 15-year prison term.