well, Derrick Harriott's 'Scrub a Dub is from 1974 and it has to be assumed he was riffing on the rub-a-dub (three men in a tub) rhyme. And every other such reference.
"Hey! rub-a-dub, ho! rub-a-dub, three maids in a tub,
And who do you think were there?
The butcher, the baker, the candlestick-maker,
And all of them gone to the fair."
or
"Rub a dub dub,
Three men in a tub,
And who do you think they be?
The butcher, the baker,
The candlestick maker.
Turn them out, knaves all three."
And what does it mean?
pr0n!
