What is the purpose of the tiny holes in the thermal tiles used on the Space Shuttle?

When a tile is glued onto the shuttle's metal skin, there must be a way to ure all the surface has glue and no air bubble gets trapped in the layer between the skin and the tile. A very small hole pes through the center of the tile. A vacuum pump's hose end is put over the hole, and air is pumped out until glue comes out the hole.