Regardless, this has already been done. Look at Cracker's mod, at Pipe element and get creative with it.

Like I just said, it has been made. Check out Cracker's mod, Pipe element. :P

With some careful planning it's easy to make a one-way wall, even a pressureless but particle-passing wall, even conveyer belts.
You have to remember which opening side determines the Beginning and End section of the pipe particles but otherwise it's flawless.

Easy. You draw a section of pipe to open space you want to be one-way. Erase the section of wall blocking the desired "Out" direction.

And then, flood-erase the rest of the surrounding brick. Particles will be able to escape in only one direction through the resulting wall.