95stepside

ok so this isnt on an F150 but the general principles apply im assuming. i have a 95 s10 with a 2.2 4 banger and the heat hasnt worked since i bought it. and for those of you not aware, its JANUARY and i live in IOWA lol. replaced the thermostat today and it solved another temp. issue but not the heater. talked to my mechanic and he said to do a back flush. he said to remove both hoses and run water through both holes, switching from one to the other until clean. is this the proper technique?