Drinker's toast is another pub's motto (7,2)
I believe the answer is:
bottoms up
'drinker's toast' is the definition.
'bottoms up' can be an answer for 'toast' (I've seen this before). I am unsure of the 'drinker's' bit.
'another pub's motto' is the wordplay.
'another' is an anagram indicator.
'pubs'+'motto'='pubsmotto'
'pubsmotto' with letters rearranged gives 'BOTTOMS UP'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for bottoms up that I've seen before include "Your good health!" , "Toast" , "down it goes!" , "Down the hatch!" , "Cheers!" .)