One of the most useful design elements for environmental bathrooms is a dual-flush system. Dual-flush tanks offer two choices: a low-volume flush (usually 0.8–1.1 gallons) for liquid waste and a higher volume flush (approximately 1.28–1.6 gallons) for solids. http://socialtuberss.epizy.com/read-blog/3148_why-flush-tanks-are-essential-for-modern-plumbing-systems.html