The habit I’ve developed, which seems to create the most in-tube length for me, is as follows. I use an air pump with gauge, quick release valve and battery operated pump - its very handy. I always try to go into the tube hard - 95%+. Arginine helps. I start by pumping up to 6-7 inHg, hold for a few seconds, then release the pressure quickly by 5 inHg, and immediately pump up to a higher pressure by 1 inHg, I.e. My cycles look like this: 6,1,7,2,8,3,9,4,10. I always Kegel when increasing the pressure. I’m quite comfortable at 10 inHg. I’ll then spend about 30 secs - 1 min at this pressure, before dropping by 5 and increasing to 11. Repeat this kind of cycle to the highest pressure which is still reasonably comfortable, which is currently 14-15 inHg. I only spend 10 -20 secs at these high pressures though. When I pause at high pressure I’ll ‘milk’ by tugging on the tube - 30 tugs say - I Kegel with every tug. If increasing pressure doesn’t result in any extra expansion it means I’m going soft. So I take it out, get hard again, and start again, albeit I’ll restart at a higher initial pressure. So long as I don’t spend too long at high pressure I get minimal fluid build up - certainly no donut. This routine creates the best stretch I can get, with minimal fluid build up. Stretching and jelqing beforehand are very useful to get into a good flexible and warm state.
I ALWAYS go by feel - if its uncomfortable I’ll stop going higher, or reduce the pressure, or simply stop pumping. I can see when I’m getting fluid build up in the tube - I’ll stop at this point. Every time I’ve broached a new maximum pressure there is always some spotting. Occasionally some sore bits, but they don’t last longer than a few days - never sore enough to prevent sex. No blisters yet.