end 305 is located at the bottom of the tank 90 in some embodiments a filter 310 is coupled to the second end 305 the filter 310 filters the fluid before it is removed from the tank 90 in operation the fluid is filtered through the filter 310 before traveling up the pickup line 115 the filtered fluid then exits the tank 90 through the pickup fitting 140 the fluid def is then delivered to the scr 60 via the def pickup pipe 80 the def is then used with the corresponding scr 60 unused def is delivered to the tank 90 via the def return pipe 85 the unused def is returned inside the tank 90 via the return line 120 unused def is warmed as a consequence of flowing past various components of the engine via the def return pipe 85 from the scr 60 the def is warmed to a temperature high enough to defrost frozen def in the tank 90 and scr system the return line 120 includes a first end 315 and a second end 320 the first end 315 is attached to the return fitting 145 of the header 105 in order for the sensing system 125 to function properly the def surrounding and within the sensing system 125 must be in liquid form thus the second end 320 of the return line 120 is positioned in a manner that the warmed def is directed onto the sensor system 125 as the warmed def is returned to the tank 90 the warmed def sprays onto the sensing system 125 thus defrosting any frozen def surrounding or within the sensing system 125 in some embodiments the warmed def is sprayed at the.