Most (not all) of the female quick disconnect valves have a built in check valve, meaning once at desired vacuum level you can disconnect the hose.
Obviously if you have the barb type hose fitting this does not apply.
As your penis enlarges in the cylinder, the pressure increases (vacuum decreases). Once your penis size has stabilized, the vac level should also stabilize.
Not knowing what type vac pump you have, This may not apply to your situation. Likelyhood of leaks, from high to low, for common pistol style vac pump and separate cylinder is:
1) poor seal at the base. Trim pubes, lube up dry skin, keep cylinder pressed into the pubic area especially at low vacuum levels. My guess this is 75% of the leak issues.
2a) hose connections. As nice as the quick disconnect fittings are, they have weak points that can leak. The female fitting that screws into the cylinder comes loose easily. Just keep it finger tight as a wrench can easily strip the plastic threads. There is also an o ring betwen the fitting and cylinder that is easily damaged. The male fitting typically also has an o ring that can also come off or get pinched. Note that not all male fittings have an o ring. Press the hose with male fitting into the female fitting while pumping to better insure no leaks. Probably 20% of leak issues.
2b) cylinders with barb fitting molded in is a weak point. Visually inspect the barb to cylinder transition location.
3) split in the hose at either of the fittings, or any point where the hose may have been bent in a sharp angle like when storing. Older hoses are at higher risk. Maybe 3% of the leaks.
4) the pistol style vac pumps have a very small vacuum release lever that can stick open.
5) pump itself. Pump to desired vac level, remove hose from pump, keeping thumb over the hose to maintain vac level. If vac level does not change, it’s probably the pump. A pump that has sucked in fluid is likely to have a damaged diaphragm that does not seal, but may still be able to draw a vacuum as long as you keep pumping.
6) crack in cylinder. Does happen but is noticeable. Only wash your cylinder with soap and water. Alcohol and other more severe chemicals can damage the plastic cylinder.
When testing it’s often better to press the cylinder into your thigh or stomach to get a better seal.
Initial: 7” BPEL; 6” NBPEL; 5.25” - 5.5” MEG
Current: 7-7/8” BPEL; 7-3/8” NBPEL; 8.5” BPFSL; 6.5” MEG; 6”x5” Flaccid.
Goal: Improved/consistent EQ while managing ED. Secondary: maintain current stats.