OK for idiots like me here is a clear concise solution.
Start a new game on Nova Prospekt. Go through the door and turn left and go to the end prison cell (4th one). STand at the open door and equip your gravity gun. PULL THE WHOLE TOILET off the wall. (I was breaking it off and carrying pieces! dumf!) Take the toilet down the stairs with the grav gun and double back on yourself. Stand close to the hole in the wall to lure the headcrab towards you then fire the john/crapper at it and send it back to headcrab heaven.