So these two nuns are on a road trip when their car runs out of gas. Fortunately they're within sight of a gas station.
"Go buy some gas," one of the nuns says.
The attendant is willing, but the nun needs to use her own container.
"What have we got?" the nun asks her sister.
"All we have is this chamber pot."
And that's how the nun ends up tipping a chamber pot into the tank just as the biker drives by. He stops to laugh.
"Now that's what I call faith."
Then the car starts.