Upgrading for Easier Removal/Tightening
The tapered pipe thread filling plug has a square head that makes removal difficult. This is compounded by the fitting of a steel plug into an aluminum casing. A hexagon-head brass plug of the same size and thread can be purchased at any automotive store that will permit a six point wrench of suitable length to be fitted and thus promote easy removal and tightening.
(Webmaster note: this is a 3/8” NPT drain plug).