Blood carrier somehow contains drainage, one in drops (9,5)

'one in drops' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'blood carrier somehow contains drainage' is the wordplay.
I cannot really understand how this works, but
'blood carrier' could be 'aorta' (I've seen this before) and 'aorta' is located in the answer.
The remaining letters 'ascending' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?