I don’t have the storage for my Dark Elixir from the clan pass. How do I burn Dark Elixir when I have Town Hall 7?
It will fill the empty storage, and any remaining that you earn will fill it again as space frees up. After that, you can't collect more Dark Elixir from the Drills.
If you aren't sure about how to spend the dark elixir, just rush your TH to Level 9 where you need a lot of dark elixirs to upgrade your heroes alone.