Four Army veterans are spending 120 hours in portable toilet cabins for charity.
Ian Baillie, Mike Hewlett, Gary Sprakes and Chris Nicholls are raising funds for Forgotten Veterans UK.
For five days the portable toilets on Southsea Common in Portsmouth are where the men will eat, sleep and, naturally, go to the loo.
Gary Weaving, the charity's founder, said all the men had credited the organisation with saving their lives.
Mr Sprakes, 70, a former submariner from Waterlooville, said: "I tried to commit suicide four times - my dog and this charity are the reasons I am here today."
He now works for Forgotten Veterans, which has 50,000 members and a hands-on approach to helping ex-armed forces personnel struggling to cope.
Mr Weaving, who has been cheering the men on at the site, hopes supporters will spend more than a penny when hearing about the quartet's "incredible" endeavour.
He told the BBC: "The charity came from my own suicidal problems... so all I've ever done is start what I should have had myself."
When asked about the men's toilet habits during the challenge, he said: "They just close the door and get on with it - we're veterans.
"In the past I've had to sleep in a sleeping bag completely naked with a fella for 24 hours that I'd just met for body heat.
"This doesn't phase us at all."
Mr Sprakes added: "We are a team, we have the mindset that this is what we have set out to do and we are going to finish it together."
Mr Baillie, 55, from Liverpool, is a former private in the Royal Corps of Signals and Royal Anglian regiments.
He said: "It's not so bad in the day when people are talking to us, but at night there's no room, it's uncomfortable and you're lucky to get two hours' sleep."
"The worst thing is the neighbours," he joked.
Former corporal Mr Nicholls, 58, from Portsmouth, said: "Trying to sleep in here is a challenge but we have raised a lot of money and the public have been amazing."
Mr Hewlett, 55, a former rifleman with the Royal Green Jackets, said: "It's difficult to sleep in the loos, you can hear each [person] moving about, and on the first night I could hear someone shout out, 'Whose stupid idea was this?'
"But the loos are new so there's no smell."
The four men are expected to have done their business in the toilets by Sunday afternoon.
Follow BBC South on Facebook, Twitter, or Instagram. Send your story ideas to south.newsonline@bbc.co.uk.
6 things you may not realise are illegal to do at the beach
One in nine Island adults never got vaccinated against Covid
New commander of Portsmouth Naval Base insists the city and Royal Navy has an 'exciting future' ahead
Isle of Wight Festival diversions now in place
Air ambulance lands in Winchester as crews rush to 'serious medical emergency'
Life expectancy among Hampshire's poorest men more than six years lower than well-off peers
Civilians trapped in eastern city running out of water
US makes biggest interest rate rise since 1994
Saudis seize 'immoral' rainbow-coloured toys
'The war has destroyed three generations'
Russia's economy buckles up for a bumpy ride
The real identity of Babushka Z - Russia's propaganda icon
Rifts split America's abortion 'ground zero' state
Is Liz Truss right about Northern Ireland's Brexit deal?
Inside the room where Ukraine orders arms from the West
Ukrainian widow: My baby and I were kidnapped. Video Ukrainian widow: My baby and I were kidnapped
Why Afrikaans is loved and loathed in South Africa
What's happening to Bitcoin?
A tiny hotel on the edge of the world
The biggest attraction for visitors is the new perspective they may gain on life
Which plants absorb the most carbon?
Turning your garden into a carbon sink isn’t just about adding lots of trees
The 12 best films of 2022 so far
From Top Gun: Maverick to Turning Red and Everything Everywhere All at Once
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.