Hey there Mikey, congrats on your progress through school = )

I would recommend something larger than a colander, depending on the number you wish to sort. In addition, you will find that colanders with many holes that run along the entire inner surface will make sorting the larger nymphs and adults a pain in the rear, as they will simply climb up the sides and fall down into or onto whatever surface lies below.

Try a bucket - you can pick up a 5 gallon (or smaller) bucket from a store fora few bucks, and drill holes in the bottom only. This will contain all of the roaches and allow the frass to fall through while keeping the roaches contained. You an buy a couple of buckets and increase the hole size with a larger drill bit to sort larger sizes of nymphs from one another, etc.

A 1/8" bit should do the trick for separating frass from roaches... larger bits (3/8", 1/4" etc) can then be used on other buckets if you actually want to monitor specific sizes of nymphs....and obviously the largest adults can generally be sorted by hand. But a 1/8" bit should do the job for frass.