Purgative quietly swallowed by some poorly sailors (5,5)
I believe the answer is:
epsom salts
'purgative' is the definition.
(I've seen this before)
'quietly swallowed by some poorly sailors' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'swallowed by' means one lot of letters goes inside another.
'poorly' indicates an anagram.
'sailors' becomes 'salts' (salt is a kind of sailor**).
'some' anagrammed gives 'esom'.
'p' placed inside 'esom' is 'epsom'.
'epsom'+'salts'='EPSOM SALTS'
(Other definitions for epsom salts that I've seen before include "Medicinal preparation" , "a purge" , "Medicine taken for heartburn and constipation" , "Purgative" , "They should clear out!" .)