A little port tipped into wine, is less capacity than you might like (4,3)

'less capacity than you might like' is the definition.
(pint pot is a drinks unit)

'a little port tipped into wine' is the wordplay.
'a little port' becomes 'pt' (abbreviation. I am not sure about the 'little' bit.).
'tipped' says the letters should be written backwards.
'into' indicates putting letters inside.
'wine' becomes 'pinot' (eg pinot noir).
'pt' back-to-front is 'tp'.
'tp' placed within 'pinot' is 'PINT-POT'.

'is' acts as a link.

Can you help me to learn more?