What is Moisture Lock?
Moisture Lock is when small amounts of water get trapped between glass joints on your bong and seal them together. For instance, if your downstem gets placed into your bong while there is moisture around the male joint, there is a chance that when compressed, a small vacuum can form and seal the downstem to the female joint on your bong. This can sometimes keep the pieces sealed together for days, and in the worst circumstances, can keep them locked together indefinitely.
Many long-time bong users have learned the hard way about moisture lock when they accidentally break a glass joint while trying to pull two pieces apart, usually the male downstem into the female glass joint on the bong. Breaking a downstem is never a fun thing, but it is more desirable than breaking the female joint on your bong. That is essentially, unfixable, unless you can find a glass artist willing to repair it. Even then, it will cost you something. If you break the downstem, it’s not too expensive to replace. Certainly nowhere near the price of your bong.
If you find you are having this problem with your downstem, there are options like Toob Loob, which is a fine, slippery wax built into a lip balm dispenser. When you rub it along the glass joints it helps to ensure a smooth slide operation.
Stemless Bongs/Stemless Rigs have tried to solve this problem by eliminating the downstem altogether, replacing it with a built-in chamber to simply place your bowl into. Moisture Lock tends to happen with downstems. Bowls seldomly, if ever, have moisture lock issues.