Settle a debate: if you did a hole on a full moon...will you have extra dirt?

Bunch old dudes have been telling me:

If you dig a hole on a full moon and go to refill it that night, you'll always have extra dirt.

If you dig a hole on a new moon, you'll never have enough dirt to fill it up.

I say it's false unless there is some valid theory with the gravitational pull of the moon.

Old people say it's true regardless. It just is. II ask them to prove it and they say "it's true"

So, is this true or false?