This walkthrough is brought to you by the puzzle designer himself. You can find the Interception PeTI puzzle here: http://steamproxy.net/sharedfiles/filedetails/?id=69323011
After stepping into any test chamber, figuring out what to do first is often the most daunting task. But this step can be simplified by following this strategy:

1. Identify the exit
2. Locate all the resources in the test chamber--cube droppers, buttons, funnels, light bridges, etc.
3. Take a mental note of all the potential hazard in the puzzle--goo, abyss, lasers, etc.
4. Work out the steps backward, from exit to the beginning

This general plan can be applied to all Portal 2 puzzles. This is how I taught my four-year-old son how to solve puzzles, and he began cracking them right away using this approach.

For this puzzle, the exit is located in the upper level, across from the entrance area and adjacent to the bright observation room. There are three general sections of the map--the main chamber, the chamber where the laser beam originates, and the section containing the exit platform.

There is one cube dropper for each section, and each cube dropper provides an unique type of cube. There is an excursion funnel that connects the main chamber and the laser chamber. There is a hard light bridge that starts out deactivated, and there is a laser receptacle that changes the direction of flow for the funnel.

There are three turrets--one in the laser chamber guarding that area, and there are two guarding the exit. You must come up with creative ways to deactivate them, using different testing elements. There is a canal of goo connecting the main chamber area and the laser chamber.

To get to the exit section, it is necessary to activate the light bridge with a cube. To get the cube, the tester must get it from the laser chamber first. This shall be our first priority.

To retrieve the weighted cube from the laser chamber, the player simply create a portal high enough to jump into the funnel. To avoid the turret inside the laser chamber, wait until the funnel carries you to the end of the tunnel leading into the laser chamber, and jump down. Use the platform that the turret cage is situated as a barricade, and deactivate the turret using the funnel.

Use the switch inside the laser chamber to drop a reflectocube into the funnel. Use the reflectocube and the funnel to drop the weighted cube in the chamber. Redirect the laser into the receptacle to reverse the direction of the funnel and exit the laser chamber with the weighted cube.

First, travel to the light bridge button yourself before bringing the weighted cube to the button. You may need to place the weighted cube in a strategic location to be able to retrieve it remotely once you are on the platform of the light bridge button.

Use the light bridge to arrive at the exit platform area. Consider adjusting the origin portal of the light bridge to gain extra height. This step is perhaps the least intuitive but also the most creative aspect of the puzzle.

At last, you have finally arrived at the exit section. First, you'll need to deal with the threat of the twin turrets. In the process of taking care of turret business, you will need the weighted cube from the light bridge button. Retrieve the cube remotely using the funnel.

After you procured the precious companion cube, use it in concert with the weighted cube to activate the light bridge again. You will need both cubes to be able to achieve this goal. Put either cube onto the button that activates the exit door, and put the other to activate the light bridge. You may need to re-use some of the puzzle elements to get both cubes in their proper positions. It is not necessary to leave the exit platform to position these cubes correctly.

Finally, you need to devise a way to activate and de-activate the exit button remotely to bypass the double-door trap at the end. I don't want to spoil it for you, but consider all the puzzle elements in the level. This is not a test of quick reflex. Approach this puzzle logically, and you shall be rewarded with a gratifying solution.

The sweet taste of success is within reach. Good luck.