It’s a tricky tactic that can help you take a city before the defender can realized it and prevent him to use the curfew command.
To make the train work you need 5 lobbyist (4 for wei) or ask player of your league to help you by attacking with some lobbyist too.
The train is quite hard to do since you only got 6 schedule deployment and you have to have 5 different attack with a lobbyist, your clearing wave and your demolisher wave.

First : check when your lobbyist and demo of all your city take to get to the target. If the difference of time is less than 10 minutes you should be fine to launch them at the same time.

Second: Pick a time that you want the attack to land or just launch the attack that from the city that the farthest from the target, note the times of that attack will land

Third: Time your clearing wave and demo wave to hit before this time, the clearing wave first and the demo wave a few second after. Make sure to hit the annexe and that you have enough demo to clear the annexe.

Fourthย  : Launch all the other lobbyist attack so the land after the other attack by less than 5-10 minutes, if you have enough schedule deployment left use them.

If everything go fine you should have the city in one sweep.
To increase your chance you can always fake a train by using fake attack of demolisher since they have the same speed.

Another variant you can do : attack normally with a clearing wave and a demo wave and clear annexe of their cities. And after send a train with a clearing wave since that only 5-6 attack it’s easier to do, but since you’ve cleared there annexe they probably think you want to steal there city.

Hope it’s help.