Rubber plug for wood worm treatment

The plug is used to seal the end of 10 mm bore holes in a wooden beam, so that it can be filled with liquid for woodworm treatment. One of the beams in my hut needs it desparately.
Due to geometrical limitations I can only drill nearly horizontal holes. Filling these without a plug is not possible, because the liquid would simply flow out. 
 

The hexagon pocket in the plug is needed to make placing the plug easier.
There is a small slot at the outer perimeter, so that a syringe needle can be fed through, once the plug is in place. 

Using a syringe, the hole can be filled with liquid.

I printed with 4 perimeters and 5° higher temperature using Filatex Flex40.