Comments by "" (@neutronalchemist3241) on "Thunderf00t" channel.

The "secret" is to use the pressure, not fight it. IE the Trieste bathyscaphe had an acrylic window. It had a truncated cone shape so that pressure pushed it against the hull, aiding its air-tightness. The rim of the titanium ring should have had this function, but you can see that it was too thin. The structural integrity was almost entirely delegated to the glue.
2