some thread sealant on the threads of the machine screw should make it air tight
View attachment Loctite_Straight_Thread_Sealant_STS-EN.PDF
http://tds.loctite.com/tds5/docs/sts-EN.PDF
Brian
View attachment Loctite_Straight_Thread_Sealant_STS-EN.PDF
http://tds.loctite.com/tds5/docs/sts-EN.PDF
Brian