I have had a few tubes fail flat in the middle of a ride, even when they were fully inflated at the beginning. When that happens, and the tube isn't punctured, I re-inflate them, but change to new ones as soon as I get home.
Is that a sensible approach? When I inflate them outside of the wheel, there is no sign of damage, or bulge. How much should I trust a tube that has failed me? Right now, they are in the purgatory box for emergencies.
It has happened with both Presta and Schrader valves.
If the tube looses air, then its coming out somehow.
Check your tube for a hole by inflating it to about 2~5 PSI outside of the tyre, and if the hissing of air isn't heard then submerge it in a tub/sink of water. The air bubbles show where you need to patch.
If the tubes all have holes in the same place relative to the valve, then look at your rim/tyre and find the cause.
It is not uncommon for a small fragment of glass or wire to hide inside the rubber of the tyre and repeatedly puncture the tube, and then retreat into the rubber when you're not riding. Inverting the tyre can help, and work under bright light.
If you can't find a hole, check the valve. They can sometimes leak slowly, but the water-test will show that.
If you're disposing of tubes, then that's wasteful. A patch costs somewhere between 20c and $1 (roughly) and a tube costs $4 to $20.
Patch a $10 tube twice and you have saved yourself about $18.
