I took that post to mean that with CET fitted there's nothing stopping you from boarding a train that isn't due to move for a while, using the facilities and flushing while it's in the station...
The downside of that being that it fills the tanks up, meaning that train will have to run with the toilet being locked out!
Now if somebody can invent an efficient motor powered by burning the contents of the tanks, they'll be on to a winner. TOCs could even give vouchers for 10% off your next trip that get printed out of a device when you flush!