Until after WW11, In England most city houses had no interior toilets. Instead they had a small hut at the bottom of their garden.

John's dad says - Johnnie, who pushed the toilet hut into the river?
Not me Dad.
Now listen son, I'm gonna tell you a story. When the great American leader, George Washington, was a lad, his Dad asked him - George, who chopped down the cherry tree? George said - father I cannot tell you a lie - it was me. Well son, says his Dad, I admire that attitude, and because you told the truth I will not punish you.
So I will ask you again - who pushed the toilet hut into the river?

I cannot tell you a lie father, says Johnnie, - it was me.

Whereupon his dad gives him a good thrashing.

Afterwards Johnnie questions his father - but George Washington told the truth so went unpunished, when he chopped down the cherry tree.

Right, says his dad, but George Washington's Dad was not sitting in the cherry tree at the time.

Good one, Del Boy!

Nice one.