Thank you both for the info. I have 1993 Winnebago Itasca, Same problem.
I removed the pull ring on the winterizing valve and pushed it out of the bottom of opaque down tube. I found 3 o-rings, thought how hard could it be to find new ones. "WRONG" there are as many o-ring ID / OD and more thicknesses as there are people on earth, probably more!
Heading down to Ace to get the parts you listed. I will have to add the valves that redskinman used. Where I live we get as hot as 116 summer and 20 - 30 winter.
Hey check under your couch if it is like mine there are 2 more winterizing valves there.
Thanks