jparker66:
On the gray water dump valve I used a fairly large diameter hose clamp that was large enough to go around the dump valve and an existing nearby bracket that holds the propane tank. On the black water dump valve I reused an existing metal straplike holder that came with the original setup and this was secured to a frame cross member. I'm not sure but maybe they may be available at rv supply stores? I know, this is not very clear but the bottom line is both valves are very secure and there is no flex at all.
My initial concern was with the clearance between the bottom of the valves and the ground which is about 10" but so far it has not been a problem. I think each rv will have different needs and you'll probably have to be creative with this project which I think is very straight forward. Good luck!