Leo To always made it to the men's room, but admits he had some close calls. The creator of Toilet Rush is explaining what inspired the app that informs users about their nearest public lavatory, and its condition and amenities.
"I often couldn't find a toilet," says the 31-year-old tech entrepreneur. "I'd have to queue at a restaurant for a drink, hopping with desperation."
With Toilet Rush, those days are gone. The Chinese-language app, which has been downloaded more than 100,000 times and been No 3 in the Hong Kong Apple app store, uses GPS data to help users search for toilets within radiuses of 150 metres and upwards.
While the app began with just 200 toilets, entered by To and his team, there are now listed 4,000 places to pee, thanks to user-generated content.
The secret, he says, is its ease. The app is free to download, works on Android and iPhone, and does not require users to sign in - "When you need to go there isn't time for that."
Consequently, it's simple for those who find a new loo to rate and locate the facilities while they are in the cubicle.
Icons next to the plotted toilet indicate whether there is toilet roll, drinking water and the average waiting time. There is also a comments section.
"Some people write, 'There is s*** all over the walls', others say, 'This toilet is for gays'. I can't verify all these comments; we have to trust the users," says To.
By the rules, any loo the public can access for free and is not in a private space is a public toilet. "If it has a key, but there is a way to get it, it's public."
So while there are 1,600 government maintained public toilets, Toilet Rush has charted another 1,400 in parks, near MTR stations, in shopping malls and even one on a roundabout.
Perhaps the sheer variety of toilets in Hong Kong has fuelled the app's success.
Take the controversial "five-star restrooms" at tourist sites, such as the HK$2.8 million facility at Lam Tsuen Wishing Tree, which resembles a roofed villa, or the landmark loo overlooking Tsing Ma Bridge, which boasts a waiting lounge and piped-in classical music, that cost HK$10 million - this is the favourite of Lo Wing-lok, chairman of the Hong Kong Toilet Association.
At the other end of the spectrum, a toilet in Celestial Heights mall in Ho Man Tin came up a little smaller than planned, with eight urinals crammed into 2.5 square metres - meaning buttocks would brush if the facilities were full.
A quick app check, it seems, can dramatically affect the surroundings in which you relieve yourself.
Dedicated Toilet Rusher Desmond Wong knows this only too well. The 26-year-old discovered the app after developing an upset stomach during a stressful period. "One morning I was in the loo and thought, 'I can't be the only one looking for a toilet in desperate times'," says Wong.
However, he dispels rumours that the app is used by the gay community to find partners. "It's Toilet Rush, not Grindr."