You can diy by buying a diamond hole saw bit( got mine off of ebay). I drilled three holes in my tank and one in my sump. Cost for the bit was less than 20 and built my own internal c2c overflow out of plexiglass.
If you don't feel safe drilling or have it drilled. Look into CPR overflow box. I used one for 2.5 yrs with no problem. Just make sure the aqualift tubing is black to keep alge out and clean it every 1-3months.
I can also drill it if need to be or you can use my bits.