Catholic building in wet field went with the flow, mopping up rug (6,6)

'catholic building' is the definition.
(nickname for Liverpool's Metropolitan Cathedral)

'wet field went with the flow mopping up rug' is the wordplay.
'wet field' becomes 'paddy' (paddy is a kind of field. I am not sure about the 'wet' bit.).
'went with the flow' becomes 'swam' (went with the flow of water).
'mopping up' indicates putting letters inside (mop up can mean to eat or consume).
'rug' becomes 'wig' ('rug' is an informal term for a wig).
'swam' going around 'wig' is 'swigwam'.
'paddy'+'swigwam'='PADDYS WIGWAM'

'in' acts as a link.

Can you help me to learn more?