Most obvious to me is:

CATS ON THE ROOFTOPS (2)

When you wake up in the morning with the devil of a stand,
From the pressure of the liquid on the seminary gland,
If you haven't got a woman you must take it in your hand,
As you revel in the joys of masturbation.

and

Native American Nell
That is the land where they understand
what it means to copulate,
Where even the dead sleep two in a bed
and the infants masturbate.

But you'll find quite a few more if you just go search the database on the single word masturba* (I think it's easier in the DOS version.

Give me a few days to get my computer back (finally) and I'll search my rugby & SCA files. Ellenpoly's line seems familiarly from there.

If wet dreams count, I've never been able to think of the verse in "Rambling Irishman" as anything else. Well, who knows? It would be the missing 4th verse in the DT version...

The first night that I spent on board,
I dreamt about my Nancy
I dreamt I held her in my arms
And well she pleased my fancy
But when I awoke from my sleep
And found my bosom empty
Well you may be sure and very sure
That I lay discontented.