Get grime off a sand-glass (3,5)
I believe the answer is:
egg timer
'a sand-glass' is the definition.
(I know that egg timer is a type of sandglass)
'get grime off' is the wordplay.
'off' indicates an anagram.
'get'+'grime'='getgrime'
'getgrime' anagrammed gives 'EGG-TIMER'.
(Other definitions for egg timer that I've seen before include "Possible kitchenware" , "device for boiler" , "Sandglass that runs for three (or four?) minutes" , "Small kitchen sandglass" , "Mechanism on for, say, three and half minutes?" .)