Lag once around a tank, one hollow (10)

I believe the answer is:

excavation

I'm a little stuck... Click here to teach me more about this clue!

'hollow' is the definition.
(thesaurus)

'lag once around a tank one' is the wordplay.
'lag once' becomes 'excon' (I have seen 'Old lag ' mean 'ex-con' so perhaps 'lag' could also mean 'ex-con'. I am not sure about the 'once' bit.).
'around' indicates putting letters inside.
'tank' becomes 'vat' (type of container).
'one' becomes 'i' (Roman numeral).
'a'+'vat'+'i'='avati'
'excon' enclosing 'avati' is 'EXCAVATION'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.