???How are the plastic things that came with the set used for inserting smoke fluid? Instructions are rather vague.
If the plastic things are the smoke deflectors that go on either side of the front of the engine they are not for inserting smoke fluid. Just a few drops of smoke fluid goes in to the smoke stack from the top.
The smoke deflectors were used on the real thing to make the smoke go higher so it would not go into the cab of the engine and smoking out the engineer.