Every time we change oil in our class C they charge us extra

Used motor oil is considered hazardous waste. that means proper disposal is required. Where I purchase our oil, they will take back your used oil, free of charge, but different states have vastly different regulations regarding the disposal of oil, batteries, antifreeze, tires, even your old oil filter's. So next time you purchase your oil, ask about disposal options. Our quick service oil shops charge a fee for oil and filter disposal.
Just don't dump it on the ground, or down the drain.