In my experience, as long as the snake is drinking there will be some waste. Although it may be minimal..
One example of this would be during hibernation. Even though you hold off food for a few weeks prior to hibernation and the animal has been down for 6/7 weeks it is not uncommon for them to still expel some waste. At least mine have been doing so for the last 16 winters..
Regardless of any of this, if an adult snake stops eating for an extended period of time and you don't know why a vet visit is in order prior to force feeding. Would you not agree??
~ Mike Russo