The term pound sand originally referred to the degrading job of filling rat holes with sand. However, its meaning has evolved, it now refers to a technique used in Vietnamese whore houses. This technique was used when the whores would give a man a hand job and then right before
the man would ejaculate the whore would cap the penis, give it one hard
pump, and then release it causing
the man to ejaculate with such force that the it would hit the ceiling.