[Td5 Intake Manifold Design]

I want to move my SPA Boost Pressure Sending Unit location from the turbo hose to the Intake Manifold.
I am not familiar with the casting design of the Td5 Intake Manifold, but does anyone know what the actual function of what looks to be a "blow out plug" on the rear of the Td5 Intake Manifold?  And secondly, does anyone know if it would be a bad or good idea to tap that area with a 1/8 BSP tap? Is the area thick enough to handle threading?

Here is a pic of the area in question. I prefer to tap this area since it would eliminate the need to run the sending unit wires down the length of the manifold. Just a cleaner installation and shorter run for the wires. Thanks in advance. Cheers. Don