I got caught short the other day on Temple wanting to have a piss so I went to KP vs. trying the 139 Temple Thai nest.

I found an app called Toiletrush which has all the public and some private (bars, hotels, gas stations) conveniences available using location services on your phone.

It pointed me to a clean and well maintained restroom at Waterloo and Shanghai (IIRC).

I was quite amazed at the quality and cleanliness. Lots of cities it would be appallingly filthy, closed,  or full of heroin users.

Other app is called Pokeguide. No idea if it was or is related to Pokemon but it's like both Google Maps and the MTR guide in one with the advantage it shows you the best car and door on the MTR to use to exit closest to the MTR exit on your route.

The toilet finder was a great find, frankly. Google Play says they both have in app ads but I am so used to ignoring ads on free apps I can't say if they are there or obtrusive.

No sense in being caught out or having to walk excessively in MTR stations with technology on your side.