When adapting between different sizes of Viton (FKM) tubing, the metal
reducers available tend to be bright-zinc plated (BZP), even if the
that they are not. Zinc is absolutely unsuitable for hgh-vacuum
systems. Stainless steel is one of the best choices; but if BZP is all
that is available,
the plating can be removed by soaking the item in strong citric acid
solution for about ½ hour. A light coating of vacuum grease will
then prevent the adapter from rusting.