Thanks for all suggestions. The twist on valve is a temporary fix to me. When I want to dump grey water only, I will have a stinky mix with it. I prefer getting the two tanks separate with separate pulls. I guess the only think to do is put on new ones. Part are not that expensive and since most local places charge $110 an hour, I am better off doing this simple job. The main problem I have is the very tight fit as I install the last cut off valve. Last time I lowered the entire assembly as mentioned. One goes on great and the other one is tight as I must have it in place as I raise the assembly and before I can tighten the bolts.
Thanks again.