Overflow Box how?

SUMP I'm planning on using my 20G tank for as the sump for my 75G aquarium. i found this image a while back and helped me understand a sump better.



if i choose to make my own overflow, what will i need? does anyone have some sort of tutorial they followed and recommend? i don't want to drill holes onto my tank, so i am looking at over the tank overflows. the design i am following is this, because this is the only design i found that seems compatible with what i want :/,









the box is clear acrylic, i want to spray paint it black...will that harm the fish?



does anyone have a tutorial that won't require drilling holes?:banana:

thanks in advance!