Noun: A lone sock kept in a bad (yet handy) hiding space
for the purpose of cleaning up after masturbation.
Johnny was upset and embarrassed when he realized that his mother had not only found, but had washed and returned his spank sock to beneath his mattress.
A sock normally kept in the bedroom under ones bed, for the purpose of 'spunking' in to after having 'a wank'. A genuine spunksock can go unwashed for up to twelve months and hold up to four pints of jism. The original spunksock is a white sports sock with a red band and a green band around the top.
I've just put my spunk sock in the washing machine on a boilwash - it took me thirty minutes to unstick it from my bedroom carpet.