Q: What did one toilet say to the other toilet?
A: You look flushed.
Explanation: After using a toilet, you need to move the lever that sends swirling water down into the sewer. Moving that lever is called flushing. To flush a toilet is to move the lever that starts the water moving.
To look flushed is an idiom that means your face changed its look because of exercise, cold weather or embarrassment.
This joke is funny because it plays with the word flushed: what you do to a toilet after using it, or how you look after exercise.
Speaking of flushing, did you know that water really does swirl in different directions on opposite sides of the equator? Here is the proof: