Connected Pipes

Each end of the pipe needs an Entrance. Both must have the same connected pipe ID.
Set area 0 in one end and area 1 in the other end.

Make a Path with the same ID as the entrance's "Connected Pipe ID".
Each node on the path must be placed and "Value 6" in the node numbered as below:

Image of how to place the node in each pipe with its value:

If value 6 does not show up for you, then try using the original NSMBe.

The path must be connected from one end of the pipe to the other; this is just to show the placement.
You can place more nodes on the path if you need, only the first and last need the above value 6 number.
World 7-A area 2 is good for more information.

Example shapes:
Reverse L

Setting a pipe as "exit only" also works, and is used in retail (eg 7-A).