Good point, most of it is rust from the tube.... The white residue is aluminum ozide.... However, the water, plus the alkali from the soap, is an ideal medium to produce severe bi-metallic corrosion....

A thin film of grease on the aluminum valve would probably help, because it would be (mostly) contained by the O-rings when you slide the valve into the tube.... I guess you could use a shotgun swap to remove any residue....

Thanks, Sean, for the ideas.... I'll check them out....

Bob