Unka Dave! Pepsi Cola had an advertisement back in the 50's which stated "Pepsi Cola hits the spot..." I can't remember the last rhyme because everyone I knew would answer the first line with "...especially when you're on the pot!" Oh what clever little minds!

Another was "Ah ha! Sani-flush! Cleans your teeth without a brush!" Sani-flush was, of course, a toilet bowl cleaner but I can't remember if that was the product which was being lampooned.

Georgian Ag,

   Good night! Sleep tight!
   Don't let the bedbugs bite!
   If they do, hit 'em with a shoe
   Then charge them all a dollar fifty-two!

As for flatulence euphemisms could be an entirely new thread. A few:

Cut the cheese
Squeezed the cheese
Toot
Break wind
The above noted "Stepped on a frog"
Let one
Your burp went out the backdoor