You could run the waste line into the toilet but how would that work? The toilet only fills when you flush... Most people use a rain barrel to collect and then use for lawn or laundry. You could probably replicate the same for the toilet, but I honestly think it's way too much. Get a watersaver addon and you'll be much more efficient, and if you can store for laundry or plants then great. Just my $.02. I've never seen or heard of any kit that would do what you want, but I would maybe contact a water filtration company (like that come to install a whole house system) that has to deal with it on a much bigger scale. They may have other solutions.
