It's for a clawfoot tub I just bought. The faucet sits on 2 x 3/4" risers but how do I plumb and secure the risers at the floor? Here are the instructions http://www.costco.ca/images/content/...stallation.pdf. The only relevant instruction they give is "Position floor pipe into water supply tube". How do I secure the "water supply tube" under the floor? Is their some sort of special flange that I need to get?