Convicts on Sadoshima Island, much like those at the work-houses of Tsukudajima Island, were given one type of labor to perform, and so if they showed contrition they would receive a tiny sum as savings and, after many years, would be allowed to return to their hometowns), but drainage work was extremely heavy labor, and drainage laborers were so cruelly exploited that it was said they could not survive for more than three years.
佃島の人足寄場とおなじく、囚徒に一種の職をあたえたから、改悟すれば些少の貯蓄を得て年を経て郷里にかえることをゆるされた）が、水替は過酷な重労働であり、3年以上は生存できないといわれるほど酷使された。