BBD-700 flight crew reported the fuel tanks were not being routinely sumped by the maintenance crew.

Narrative

During the end of our trip the PIC text the Maintainer of the aircraft when the last time was he sumped the tanks on the Jet. He replied he never has. He has been the only mechanic taking care of Aircraft X since he was hired at Day 1. That means it has been XX months (at least) since anyone has sumped the fuel tanks. His response was Bombardier did not require it in the maintenance manual I said it was in the Ground servicing manual and showed him the specific task. I also asked him if he believed the aircraft should have been sumped regularly. He responded yes. I told him I would not be right in operating the aircraft any longer based on common sense and safety ( to include careless and reckless) until the aircraft is sumped. He said he did not have the right tool to complete task. After I explained I would not operate it until it is done; he had the tool off another operator in the hangar within 2 minutes. My PIC wanted me to video the fuel samples. The Mechanic clearly had no idea how to sump a Global even though he spent years as the mechanic for another Global. He had fuel coming out places he was not ready for it to come out. Several samples were contaminated with water.