Add 1 cup if perlite so that it creates about a 1" layer over the end of the plant starter plug and the batting/floss. Set your cutout from your bottom 4" PVC cap dead center on top of the layer of perlite, and be sure to tape over the hole that your hole saw left in the middle. Extremely critical that you put this cutout in there, or your planter will leak, I guarantee it! Don't worry, the perlite and batting/floss will create a wick around the plant starter plug and the roots will find their way around the cutout just fine.