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Ever wondered how astronauts use the toilet on the ISS in a weightless environment?

Well wonder no more, as Montana-based scientist Hank Green has explained all you could ever want to know about micro-gravity loos in his latest video.

Green explains that astronauts perform numbers one and two using a suction system, and some of the waste is reused on the ISS for life-essential systems.

Montana-based scientist has revealed how astronauts 'boldly go' on the ISS. In a video Hank Green explains how pumps are used to collect waste. When doing a number two astronauts have to sit on a small toilet seat (shown), which has a small opening. They 'potty train' by using a camera to see where to sit

'As you might imagine, it's a little bit tricky,' says Green in the video, his SciShow Space YouTube channel.

On Earth, we are used to toilet seats about 12 to 28 inches (30 to 45cm) in diameter, but in space astronauts must contend with an opening that's about four inches (ten centimetres) wide when they do a 'number two'.

They use restraints to hold themselves to the seat, which ensures that no waste can escape while they sit down and do their business.

To train astronauts to do this, Nasa has a toilet with a camera inside so they can practice positioning themselves correctly when they sit down.

'The toilet itself works like a vacuum cleaner, using differential air pressure to suck the solid waste away,' continues Green in the video.

The waste is not jettisoned into space, however, and is instead stored on the station to be disposed of on a capsule returning to Earth.

'The toilet [shown] itself works like a vacuum cleaner, using differential air pressure to suck the solid waste away,' continues Green in the video. The waste is not jettisoned into space, and is instead stored on the station to be disposed of on a capsule returning to Earth

Urinating, however, uses a different contraption.

Personal urinal funnels are supplied to each astronaut, which attaches to a hose adapter.

When an astronaut uses the funnel, fans suck the urine out into a waste water tank.

'Naturally there are different set-ups for male and female astronauts and it's actually easier for the women,' explains Green.

'They can place the funnels directly against their bodies which adhere to them and then the section is turned on.'

For male astronauts it's a bit more difficult; they have to hold the funnel close enough to catch all the urine, but not so close that it might cause an injury.

To collect urine a funnel is used with a hose (shown) and the liquid is then stored. This can be recycled using an anti gravity machine for drinking water, and Nasa hopes to eventually also use it to produce electricity

The ISS (shown) supports a crew of up to six, with crews split into groups of three. The station orbits at a height of about 265 miles (425 kilometres). It has a total mass of about 990,000 pounds (450,000 kilograms) and has liveable space roughly equivalent to a five-bedroom house

Toilets on the ISS aren't cheap - they can cost upwards of £11 million ($19 million), while the entire set-up costs about £150 million ($250 million)

This is because the urine facilities are fairly complex; in 2008 astronauts began using a new system than can purify and distill urine into water.

This can then be recycled and used for drinking and bathing.

To separate contaminants in the urine from the water, the ISS has a spinning keg-sized distiller that creates artificial gravity while boiling the liquid.

Eventually Nasa also hopes to generate electricity using the urine in a process known as forward osmosis.

'Now if only we could find some equally useful thing to do with our space poop,' Green concludes.