What do I need to destroy to get all the Dark Elixir in a village?

I want Dark Elixir.

My question is, if it is shown that 1000 Dark Elixir is available as loot in someone's village, and I destroy his storage with lightning spells, will I get all 1000 Dark Elixir, or do I need to destroy the Dark Elixir drills and the Town Hall too in order to get it all?

Solution 1:

As per the Version 7.156 - 2015-07-01 "Dark Spell Factory" update:

All resource storages are now immune to all direct spell damage

This means that you will never damage or destroy a Dark Elixir Storage building with lightning spells (or earthquake spells).

As for the other part of your question, the 1000 DE available for loot shown is from all possible sources combined - this includes the DE storage, DE drill(s), Town Hall and the Clan Castle. So yes, you would need to destroy all those buildings to get them all. See How do I tell where loot is stored? - for more info on which buildings are holding the most resources.

Solution 2:

In order to get all the dark elixir, you need to destroy the town hall, drills and storage.

The amount of dark elixir you obtain from a storage is 4 times greater than the amount you obtain from the town hall.

The amount of dark elixir you can obtain from a drill is 75% of its current capacity.

So to get a rough estimate of the amount of elixir you can get by destroying the storage, divide the dark elixir amount by 5, then multiply it by 4.

Reference : http://clashofclans.wikia.com/wiki/Raids