从马桶冲走
to get rid of something by putting it in the toilet and operating the toilet
  I tend to flush old medicines down the toilet. 我往往用马桶冲走过期药品。 
 Please do not flush sanitary products down the toilet.
 I have a suspicion that the student flushes his lunch down the toilet.
 They were accused of flushing contraband down the toilet before police arrived.
 He tried to flush a flannel down the toilet and clogged it.
 He had ripped up the document and flushed it down the toilet.
 See also: flush verb (TOILET)