(Quoted from Brian Walker & Printwear magazine. Full Article Here.)
You can pretreat by hand, but the variability of manually pretreating can cause issues. One issue is that you really do not know how much pretreatment you are applying to the shirt, which is one of the most important aspects of properly pretreating—specific amounts of pretreatment are required to get “the perfect print.”

Click here to read the full article