How big are the snakes?
T. Butlerii from my area only get about 20 inches long, and slimmer than my ring finger.
Two live happily in a med cube exo-terra with a bioactive substrate, but their water dish is cerial bowl sized. (Less than 1/4 total floor space. The isopods are very good at cleaning up waste with little help from me, and the snakes spend lorlts of time up sunning in their extensive branch and reed penthouse.

One big eastern or checkered might be too much for this setup, and my checkered wouldn't do well with the moist substrate.

Id like to take an entertainment center, or a 50-100 gallon enclosure and set it up with a very good small hand basin from therecycling center plumbed thru the floor so the water could be drained and cleaned into a bucket beneath.

Mi herp zoo has many of their large reptile enclosure set up with what are essentially naturalistic looking bathtubs, so they can easily be emptied, cleaned and refilled. I like the idea.
I guess I don't know enough about turtle filtration systems to trust them to keep the water really fresh and potable. It may look clean, but im not sure about purity. I don't want a parasite reservoir lurking in my filtration.