a riddle

Swings by his thigh, a thing most magical!
Below the belt, beneath the folds
Of his clothes it hangs, a hole in its front end,
stiff-set and stout, it swivels about.

Levelling the head, of this hanging tool,
its wielder hoists his hem, above his knee;
it is his will to fill, a well-known hole
that it fits fully, when at full length

He's oft filled it before. Now he fills it again.