Sentence:  During an early river trip back in the 1970s, shortly after this system was developed, the toilet seat was accidentally left behind, the rims of the riser left telltale indentations on everyone's bums, and the box got a nickname: the <WSD>groover</WSD>. (Some guides also call it the duker or the unit.) 
Meaning of the word marked with <WSD> tags:  A small portable toilet often used on multiday river trips in protected wilderness areas, so named because the original versions were metal boxes whose rims left a groove in the skin of the user.