The stimulation of one's own genitals, with intent to orgasm; sexual self-gratification.
I sprained my wrist doing grunt work last night.
My wife was out of town last weekend, so I got stuck doing grunt work.
I've been doing grunt work since I was nine years old.
Simple-minded, repetitive and some times redundant work.
Using a lawnmower can take the grunt work out of pruning the lawn. ;)