Question

Where does the phrase rub a dub dub thanks for the grub yeah God come from?

Answer 1

It is a funny way to pray kind of phrase, it is said in the Simpsons and Family Guy.
It also may mean before dinner you clean your hands then you eat to get the ¨grub¨.

Answer 2

 I'm guessing it's been around since at least the late 70's or early 80's.