Upon entering the chamber, you will be greeted by a Switch. Press the switch and it will drop a Weighted Storage Cube.
Using one-to-one, move the cube through the air and onto the button that's in the Goo. This will raise a platform for you to cross.
Cross over the newly risen platform and look ahead. Place a portal on the surface above and one on the ground in front of you. Use one-to-one again so that you can drop the cube through the portal on the ground and press the button.
After the button is pressed, another platform will rise out of the water. Walk across and go through the portal that was used for the cube.
Grab the cube and use one-to-one to move it into the air and around the metal grate that blocks the final button. Drop it onto the button.
