Signature Hardware 446541 Freestanding Tub Drain Rough In Kit for Cast Iron Pipe Ideal for a DIY update, this drop-in rough-in makes it easy to install a freestanding tub. The kit installs above your subfloor, but underneath your cement floor or tile, so you do not need access below the fixture. The tub's tailpiece is secured into place by multiple push-fit rings that create a water-tight seal.