The white stuff is a urate and isn't related to their feces. It's another form of their urination process and both genders pass urates. Basically they both pass three things through their vent - liquid urine, solid urates and solid feces. Urates very simply are the byproducts of their ability to recycle their own urine prior to it passing from the vent in a liquid form. They can absorb more liquids that way and just pass the leftover urate out. It's a handy thing if you're a snake that has to live through a drought and all the liquid you can get might be from your live prey item.