I am thinking about putting together an ATO reservoir. Size will be 15" x 15" x 5.5". Will 1/4" thick cast acrylic be ok to use for this? What kind of acrylic cement is best for this?
1/4 will be fine make sure like already said euro brace the top. The bracing at the top will greatly improve strength but also will give you a surface to mount an acrylic tube for a pick up and a way to create an air tight lid. Try to get the edges of the acrylic finished square and smooth enough to use weld on 4 and use weld on 16 as a last resort.