Spray paint maintenance

Hey Ive been spraying for a while now and seem to have gone through an unholy number of caps. Once done I turn the can upside down and spray for a few seconds till nothing comes out, then take the cap off and put everything away. Am I doing anything wrong here or is it normal to use so many caps? I also read that you should screw caps on, not push straight down, is this true? Thanks.

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