I used a Google images search (Whitney summit toilet) and came up with these: From BrianRxm - Sierra Nevada Peaks, Mount Whitney: (Page no longer exists) I believe the walls were destroyed by vandals in 1978.
This from SummitPost: Whitney Summit Caption: Craig on the infamous toilet at the summit of Whitney, with a nice view of Williamson to the left. Here one can have the opportunity to take the highest shit in the lower 48 Just imagine, for first time climbers of Whitney who come up the Mountaineer's route, the first thing you could see on the summit after topping out from the class 3 is this!! This thing doesn't exist anymore.