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.
Can you guess the answer (without looking it up)?