Stop to empty the bath (4,3,4)
I believe the answer is:
pull the plug
'stop' is the definition.
(I've seen this before)
'empty the bath' is the wordplay.
I cannot quite see how this works, but
'empty' could be 'e' (abbreviation e.g. on guages) and 'e' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for pull the plug that I've seen before include "Scrap" , "Stop (something) continuing - empty the bath!" .)