Green’s Dictionary of Slang

grave-digger n.1

[alcohol often proved fatal to white men in India]

(Anglo-Ind.) strong drink.

[UK] Daily Tel. 21 Aug. in Ware (1909) 146/2: Too much ‘route marching, pipe-claying, and starching’ tends to dulness and apathy, whilst it leads the British soldier, when off duty, to make too free an acquaintance with the ‘grave-digger’, as it is termed in India.