Had 2 of these issues. Using the correct drill for a 1/8" pipe tap (usually stamped on the tap) center drill all the way through. Retap the resulting hole to 1/8"pipe. The flutes of the tap should push the remaining brass through the hole. Check your depth so the sender will fit when tight just above the surface of the boss cast into the manifold...
Take your time, do it right...
Terry
