Image: A new intake/fill for the dirty tank,

also has one-way feed for the overflow from the clean. If we pump too much from the dirty to clean, it will just push it back into the dirty tank, no mess. The one-way is done by a one-way check valve with a hand operated valve as a safety. If the filling (into dirty) pressure is too much for the check valve, I'll just close the manual valve when filling.