I do clean out the frass now and again. I am a bit fussy and have several containers (with lids). I take out the larvae and beetles and put them in separate containers (different tubs for different stages of the life cycle). Then what is left in the tubs is frass made up of eggs and poop, so I have to save it for a couple weeks with some oats, let the larvae hatch, and then sift them out. After that though i have a bucketful of frass! Meal worm frass looks a lot like sand.
You can see that it is very fine compared to the wheat bran in the back ground.
Mealworm frass is an exquisite plant fertilizer – indoors and out. I do, however, recommend not having it on the top of the soil for indoor plants as it might affect your condition. Otherwise, I have not met any kind of plant – leafing, flowering, or fruiting - that doesn’t love mealworm frass. It is a natural bloom stimulant, and has high nutrient levels.
As it causes plants to excrete chitinase (see below), i don't compost it! It acts as a great natural anti fungal and i brew it up with my red worm compost and make a Tea for plants.
I will update both threads and include how to make worm tea.
Here is the scientific bit about frass.
"It causes plants to excrete chitinase due to high chitin levels, it is a natural bloom stimulant, and has high nutrient levels. Frass is known to have abundant amoeba, beneficial bacteria, and fungi content. Frass is a microbial inoculant, also known as a soil inoculant, that promotes plant health using beneficial microbes."