1-1/2" Flush Slip Fitting for gray and black water holding tanks. Icon has a wide selection of RV waste holding tanks to choose from, including 6 drain styles and many different sizes. Our tanks can be used for black and/or gray water. All tanks are available with or without the 3" spigot fitting and four level sensors installed. Fittings are constructed of durable, high impact ABS plastic with flange for solvent welding.