The eyes of the coconut are relatively soft compared to the rest of it, so you have 3 holes right there. I went ahead & drilled them, you can puncture the eyes with a screwdriver or ice pick ( boy isn't this appropriate for halloween!) but you'll want an appropriate size for drainage for the plant.
Drain the coconut milk, now drill 3 holes in the opposite end. If you are going to quarter one half, then wait & drill smaller holes for mounting, as well as drainage on the 1/4 where you think is appropriate.
I then used a band saw & cut it in half (and quarters if you want). Scrape out all the meat.
Drill hole(s) to attach a hanger. I scrubbed the inside with a bleach solution & then just left outside in the sun for a few days. Someone has mentioned soaking & rinsing several times due to the salts but I never did & I didn't have any problems.
