Clears up, removing ulcer and liquid that circulates in the vascular system (3)

I believe the answer is:

sap

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'liquid that circulates in the vascular system' is the definition.
'sap' can be an answer for 'liquid' (thesaurus). I am not certain of the remainder of the definition.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for sap that I've seen before include "Tree's blood" , "Vital plant juice" , "Watery substance in a plant" , "Fluid in plant stems" , "Plant's fluid" .)

I've seen this clue in the Irish Times.

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