Sexy Riddle

This is a 1,000-year old riddle, taken from The Book of Exeter. I know what you are thinking but is that what they were thinking 1,000 years ago? You bet. Answer at the comment

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.