Tenant expected us to pay for lost diesel

This morning a tenant put diesel in our truck. When my partner got out of the truck he noticed that the pipe was leaking. The meter was running but there was more diesel on the floor than in our tank. We asked to switch pumps and filled up the tank. We were happy to pay for the diesel in the tank but not the diesel on the floor as it is the company's responsibility to ensure that their equipment is in working order. On refusing to pay for the lost diesel we asked to speak to the manager. He took 15minutes to speak to us whilst he was he was texting on his cellphone. The tenant continued to argue with my partner and accused us of \robbing"him. Other employees also interfered in the situation of which they also passed similar comments. The manager did not calm his employees and allowed them to continue speaking to us in this manner. We were happy to pay for the diesel in our tank of which we did however"