Best technique for highlighting submarine decking drain holes?

[cantgrowup]

I am just getting started building U-boats and am looking for best/easiest method of highlighting the "drain holes" in the decking.  I do not want to use photo-etch decking.  I use flat acrylic paints and plan to spray with clear gloss acrylic (like "Future" floor polish) to seal the porous paint.... and then use a "wash" of thinned-down black.  I don't want to have to carefully touch a brush into each hole (hundreds!) to avoid getting paint outside the holes, so a brush-on wash is desired, that can wiped to remove excess.  But what is the best wash to use?  Acrylic... enamel... tempura? I've used tempura-based washes before (with a drop of detergent for surfactant) for aircraft panel lines, which allows clean up of excess.

 

What do you other U-boat builders use? All advice is welcomed!