Get some weight on it and rapidly cap it with poop (medium works best) and take it back out. Repeat consistently and instant fertilizer. If you need poop, tame a phiomia and force feed it stimberriea.

This may sound weird but I think they are really cute

Once you use them for oil and fertilizer they will get hungry so instead of wasting their weight for food keep a feeding trough nearby with spoiled meat😁

Only upgrade weight

The Dung Beetle creates fertilizer and oil when he poop are in inventory. It must be wandering to produce. To remain at that spot, place it in a cage on a foundation (ceiling = drop)