If it's an OEM heater there is no pump in it. Water circulates via the engine water pump, just like water through the rad in a car. Do you have no heat, period? Or just no heat at idle? Y-ing the return into the raw inlet hose like the diagram in post #4 is the answer to the latter issue because creates more negative pressure to help draw the from the heater. You should be able to determine where your return hose enters the engine if you just look for a hose like the supply hose.
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KBS, IBS, Bennett Wake Plate, custom wake shaper
(previous) 2001 X5, 1991 TriStar 190