at some point I was told that the decimal (or any other base) expansion of such irrational numbers as $\Pi$ contained any other number
but that can't be! if it contained all of the digits of $\Pi$, in sequence, in its fractional part, then the sequence of digits of $\Pi$ would be a repeating sequence, therefore it would be rational rather than irrational!
indeed, even rational numbers with a periodic component to their fractional expansion cannot fit in the expansion of $\Pi$