Walaber Pipes is a secret level where you play as Swampy.
To unlock it go to the menu screen (where you can choose from different stories), and click on the gear button. Then wait until in the background a scuba diver duck shows up and tap on it. Then you will be presented with this level.
To tri-duck this level first cut the dirt so the water falls in the pipe to the right, making sure that some water will still be there for a while. (there are two pipes, one at the left and one at the right where the water is). Then make a little curve so the water can get up to the first duck.
Next get some water to the bottom of the level. Get some other water to the red switch which will push the water and you will get the second duck.
Now quickly cut some dirt so the remaining water falls into the left pipe at the start of the level. You will get the third duck and then finish the level.