For the code to control the robot, see the attached file. I used Vex's programming language EasyC, which is visual block programming.
To make the robot go where you want, just lay down some dark electrical tape or other tape that is dark and is about a half an inch wide. Then just fill up the tank and turn it over so it starts to drip, put the robot next to the line so the sensors are directly above the tape, and turn the controller on.
I am hoping to possibly add something to control the water flow, and also use an ultrasonic sensor to navigate throughout the house without needing a line.
Feel free to leave suggestions in the comments.