[Tade0]

> This is an engineering necessity and not something done to make them hard to repair.

That's not entirely true. My Galaxy S8 has a user-removable SIM tray, and yet it's rated IP68.

Water has some viscosity, so it won't flow through tight gaps unless appropriate pressure is applied.

[constantcrying]

How is this relevant? Which phone does not have a "user removable SIM tray". Usually they are sealed as well. And in any case, how does this matter for the back of the phone?

[alistairSH]

He's pointing out that tight tolerances and/or non-adhesive gaskets exist. Glue/adhesive gaskets aren't strictly required to make a water-tight seal.