Stop up containers (4)
I believe the answer is:
pots
'containers' is the definition.
(pot is a kind of container)
'stop up' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'stop' written backwards gives 'POTS'.
(Other definitions for pots that I've seen before include "earthenware here" , "Gets (a ball) into pocket" , "Stop (anag.)" , "Ceramics; pockets (ball)" , "Preserves" .)