Water does not compress when inside an internal combustion engine.
Your best option is to leave the hole open to the atmosphere to drain water from the inlet charge of the engine.
If you become more obsessed with the opening put some sort of screen underneath the opening to make you feel more secure, but leave it open to the atmosphere.
If the hole was whole it wouldn't be a hole and thus never needed, but it is needed, so best left alone to be hole.
Originally Posted by fishEH
Round piece of plastic and some silicone? Body plug and some silicone?
Do NOT FOLLOW THIS ADVICE!
Again leave the hole alone, like it is a power that is not understood, but a requirement for a healthy existence.