If their adults, you should be able to cut back the amount of food they're eating.

I feed Large rats every 2 weeks, once my supply is up, it's back to mediums every 2 weeks.

I have HEARD of a guy thinking soft water was beneficial in keeping these snakes regular, I haven't had the chance to do try it out yet.

I actually don't even pay much attention to their pooping habits any more, I know they'll go when they need to, and as long as they're eating, I don't worry.