Rotationally molded polyethylene holding tanks from PolyPortables are often used under on-site office trailers, but have also been used for temporary waste storage in other applications. The 250-gallon low-profile tank is 18 by 48 by 72 inches and weighs 100 pounds. Four clean-out ports are typically installed on each tank – two on the top in opposing corners and one on each end. Custom tanks with as few as two ports are available. A uni-seal grommet and threaded PVC connector are inserted in each port. Also available is a 300-gallon tank (18 by 48 by 90 inches) with one 10-inch manhole, two 3-inch spin-weld ports and two universal clean-outs. Tanks can be daisy-chained to increase capacity. 800/241-7951; www.polyportables.com.