Depends on the order. We use a GTX, and all I do is heat tap white shirts for like 8 seconds and print it with no pretreat. The GTX has a setting to print the colors twice on white tees, almost like double stroking a screen print. That works fine for most orders. For high end samples we do a light pretreat to help make the colors pop a little bit. Have not had any issues with washability while using pretreat. Granted we aren't Nike, but we have conducted around 10-15 wash tests on a garment that faded an amount that should be expected. Print held up well overall.
To reiterate Dan's point, if the garment is 100% cotton and the same style as the black tees, why would pretreating it the same way effect the durability? Doesn't make sense to me, I have never heard of that. Hope this helps.
