Two key ingredients to pretreat are salt and glue. It will stick to everything and rust out metal. If you pretreat by hand with a paint sprayer, then you want to be in an isolated area not around your printing equipment. For health reasons, wear a mask. You don’t want to breathe this in.
There’s been a trend over the past several years where people are investing in a pretreat machine immediately. There are many benefits to this with some of the main ones being a cleaner process, consistency, precision, repeatability, less waste, and a much smaller learning curve.