I dimension it as if it were a blind hole, with the projection dimension toleranced accordingly. I add a note to the hole, something to the effect of "pilot drill thru" or "vent hole as required" but you have to keep in mind your intended audience.
If you think the person may use a hammer to pound a dowel into a blind, press fit hole, you can get a shattered dowel, or a high speed projectile, if the pressure builds up enough. Saying the vent hole is "as required" may be taken as an optional feature when it should be mandatory. I say "as required" to only indicate that I don't really care how big it is, so long as the dowel is functional as shown in the drawing.
Hell, if all the important machining is done from the opposite side, they may desire an OVERSIZED counterbore to a certain depth, then drill and ream the rest of the way for the press fit. I try to leave it open _when it suits the design_ to let people make the part as cheaply/quickly as possible, within my requirements. But... without a supplier or shop relationship you're comfortable with, you have to go the 'legal eagle' route like KENAT specified quite clearly.
