I think you may have been referring to this one...there are "nicer" ones, but this my favorite!
There once was a man from Nantucket
Whose d*ck was so long he could suck it
He said with a grin
As he wiped off his chin,
"If my ear were a c*nt I would f*ck it!"
I found the cleaner version:
There once was a man from Nantucket
Who kept all of his cash in a bucket.
But his daughter, named Nan,
Ran away with a man
And as for the bucket, Nantucket.