0,03 % – that is one flight. Many over 3 hrs. When I was younger, the planes I could afford were too uncomfartable. Now, when I am not so young, my bladder is the limiting factor.
8 flights out of about 1,500. Longest leg 6h35 (headwind).
The MX-7-180, like any other bushplane worthy of the name, holds fuel for about 8 1/2 hours. However, I usually plan for less than half of that, because with no fuel uplift it only takes a few minutes to land, use a civilised bathroom, and score another “free” Cap Calaisis ball pen from the delicious lady in the office. 
I’m quite certain it’s 0% non stop.
With one stop in the middle it’s more frequent.
8 flights – all between 4:00 and 4:30. That would amount to about 4-5% of my flight time. It was actually more than I thought it would be.
And at risk of drifting this discussion sideways, I wonder whether we’re just as alert at the end of a 4 hour stint, even if only supervising an autopilot.
The early 180/182/185/205 all had around 55-62 USG useable which translated to around 3:30 with reasonable VFR reserves. They then went to 80 USG plus, but was never sure why you would want to be up for the 5 or 6 hours this implied (longer at 45% power).
I think the utility of large fuel tanks is as much in being able to fly to a place which has no fuel, and back, as in being able to plan longer flight legs.
Leafing through my logbooks I find many flights in the 3 hour region and many more around 2-2.5, but only two above 4 hours. One at 5.1 and the other (actually the return flight) at 6.1 hours. Both were in a C182RG with long-range tanks and were between KSMO and KALS (southern Colorado). The return flight had strong headwinds and for various reasons (mainly to avoid being over hostile desert territory at night) I decided to throttle back and fly it in one go instead of stopping to refuel. Landed with about 1.5 hours in the tanks.
On a very quick add-up of my last logbook, since July 2012, 890hrs, 461 flights, of which 60 flights were over 4hrs. Longest one about 8hrs but those are very rare. Many in the 5hr region which is the typical flight UK to the Adriatic.
I use the plane to get interesting flights to interesting places, so I avoid pointless stopovers. It is also much safer.
I would not plan a flight over about 6hrs but often the headwind is stronger than forecast, and then I fly according to the forecast landing fuel on board from the totaliser, working down to 15 USG (1.5hrs) reserve but this depends on how many airports are available near the destination, the wx, etc. There is no point in landing after x hours, when you will just have to take off again and still fly the whole required distance!
I would not go over half tanks (say 4hrs) without the fuel totaliser working.
The toilet endurance is not related to anything One has to have a provision for a pee; if you don’t, one day you will bitterly regret it. Women can generally go on for much longer because they don’t have the problem of an enlarged prostate which squashes the base of the bladder which most older men get But if you think you can normally hold it for say 3hrs, wait until you have had one coffee too many, a few cups of tea too many, and then do a 1hr flight in darkness in the winter…
Peter wrote:
The toilet endurance is not related to anything One has to have a provision for a pee; if you don’t, one day you will bitterly regret it. Women can generally go on for much longer because they don’t have the problem of an enlarged prostate which squashes the base of the bladder which most older men get But if you think you can normally hold it for say 3hrs, wait until you have had one coffee too many, a few cups of tea too many, and then do a 1hr flight in darkness in the winter…
Having a provision is one thing, using it is another, especially in mixed company. Whether one has a provision or not, it is indeed interesting how many thread entries here make reference to bladder limitation determining max trip length. 
Flying for customers where some sectors are 5 hours plus, you still need to plan for bladder endurance. One poor crew member used the facilities on a new jet, which were in the rear, the owner promptly changed crew and type for a model with facilities in the front of the cabin.
Peter you are a champion at 30% of your sectors (based on total hours) being over four hours. Perhaps you sport some top gun equipment like this?
