Fred, If you have the washer in between the flat on the stem and the flat on the tailpiece/hose barb fitting the only problem would be a need to put an open end wrench on the stem and tighten er down a hair more. So order of op should be flat of bev out stem, washer, tailpiece/hose barb, then wing nut.
The only other thing is if you are using a threaded “hose” barb fitting then their is another issue I will have to detail for you.
http://www.northernbrewer.com/shop/tail ... 4-mfl.html
http://www.northernbrewer.com/shop/1-4- ... l-nut.html
See these fittings for an example, I use these on my cold plate system as I disconnect the lines often for cleaning.