I bought a lock&lock to store medicines to avoid moisture. I put dryer inside and frequently and quickly the dryer is full of moisture and I have to replace it. Then I take a look at the plastic and flat surface where it touches sealing rubber, and find several carving mark. It looks like during manufacturing the carving mark is to remove molding line that may disable seal. But, it looks carving too much and possibly damage the surface and disable seal. So I check another newly arrived lock&lock and find it has the same mark. I bought them online cheap and I worry about they are defect product. Is there any way to test sealing leakage with common home tools?
Seal one up with just air within, and submerge it very gently in a bowl or sink full of water. We use Lock & Locks, I would expect them to hold, though I'd only test very gently about an inch or two (2-4 cm) below the surface because they're not designed for this.
Also, I do have to wonder if (a) you were sold seconds or defectives on the cheap, or (b) if the air humidity and temperature situation you have is producing condensation. The seal in our Lock & Locks is good enough that I have seen condensation sometimes in unexpected fashion. I have also seen enough online to wonder if there are counterfeits out there.