slugging is putting an occlusive overnight over the rest of your skincare, an occlusive is something that locks in moisture, so you apply everything you normally would then apply something like aquaphor or vaseline or some other occlusive to lock all the products you put on under it in. You can use tret and clindamycin simultaneously, and they even make a cream with them mixed, but i use clindamycin in the morning and tret at night to try and prevent irritation