I 1st make a template using thin cardboard or thick paper, then using a hole punch, punch out holes on the template. Then hold the template up to the tub and mark each hole with a Sharpie.

Take the tub outside in a well ventilated area to melt the holes. The fumes smell bad and are toxic so do it up wind.
Then using a cheap soldering iron, like this http://www.amazon.com/Mastech-Watts-...1906802&sr=8-7 that you can buy from a local hardware store for around $9 or less, melt out each hole.