Q: While in their tank, what did one fish say to the other fish?
A: Do you know how to drive this thing?!

Explanation: If you have a fish at home, it is in a tank: a fish tank (also called an aquarium).  Normally when you hear about a tank and fish, you think of a fish tank.  A fish tank is a glass box that holds water and fish.

The other type of tank is a military tank.  If you are in a military tank, someone has to drive it, like the fish in the joke.

This joke is funny because the word tank has two meanings: a fish tank and a military tank.  This joke misdirects us to start thinking of a fish tank, when actually the fish are in a military tank.

Here is how to take care of your goldfish in a fish tank: