It is a question that has baffled travellers for years: Where does the toilet waste go?
And, the answer may completely shock you.
Pilot Patrick Smith in his book "Cockpit Confidential" answered the question: “Are the contents of airplane toilets jettisoned during flight?”
He wrote: “Several years back, I was on a train going from Malaysia into Thailand when I stepped into restroom and lifted the toilet seat.
“I was presented with a mesmerising view of gravel, dirt and railroad ties all passing rapidly beneath me.
“Those who travel will encounter this now and again, and maybe it’s people like us who get these nutty myths off and running.
“The answer is no. There is no way to jettison the contents of the lavatories during flight."
According to the Express.co.uk, a “combination of the vacuum, a small amount of blue sanitation liquid and non-stick coating are what helps wash waste away”.
The website spoke with Tony King, sales director at SkyKem, who shed some light on the matter.
King, who supplies hygiene technology to the aircraft industry, said: “There is an airtight flap at the bottom of the toilet bowl to hold the vacuum. When you flush the toilet this flap is released and the sudden aggressive noise is made by the vacuum sucking out waste. The toilet systems are emptied by vacuum to a large waste holding tank shared by many toilets.
He added: “The vacuum is generated inside the waste tank so that waste and foul odours are all sucked into the tank.”
Smith in his book revealed: “At the end of a flight, the blue fluid, along with your contributions to it, are vacuumed into a tank on the back of a truck.”