We have an air ambulance Lear 35 for a hangar tenet, and one of the pilots ran into some stomach trouble on an empty leg back home. So, he decided to let 'er rip in the lav, in full view of the two EMT's and the f/o. What he didn't know was that the actual lav itself was removed, so there was just a toilet seat on top of the cavity where the lav unit is supposed to go. When they got back on the ground, the pilot asked us to clean it out. Thankfully, we have a company policy that we don't clean air ambulance aircraft. So, the pilot just left it to bake in the South Florida heat. They had a flight later that night, and when the other crew showed up and popped open the door, you could smell the stench on the other side of the airport. The captain on this flight asked us to clean it out, and we told him we couldn't. He threw a fit, was yelling and screaming on his cell phone at the pilot that left the mess, and the EMT's would not go anywhere near the plane. He ended up giving one of our line guys $20 to clean it out with a shop vac.