Tsukiji market is divided in two main parts. One is for meat and fish products (mainly sea food, though) and the other one is for fruits and vegetables. Because selling and buying in Tsukiji is done in large quantities the market itself looks more like a big warehouse with many boxes stacked everywhere around. It has large open spaces, but some areas are divided into small shops and tend to be more crowded.
Tsukiji opens early in the morning (around 3-4am) and closes around noon. Morning hours are very busy, which makes dumpster diving quite difficult. The best time for freegans to visit Tsukiji is from 8-9am till 1-2pm.
Tsukiji market is a very popular tourist attraction. It might be one of the reasons why nobody really cares if random people walk around.
There are at least three market places where trash is left:
2) Boxes inside the building. Usually they are put randomly in piles near the walls or columns. It is always worth checking whether they are empty or not. Some wholesalers throw away the whole box of fruits and vegetables if they see that half of them (or sometimes even less) gone bad.
3) Boxes outside the building. It's possible to find piles of boxes outside the building, too, especially after 10am or later. Many of them are empty, but some are not.
One can also find fruits or vegetables lying just on the ground. They are usually lost while transporting the boxes.
Boxes on the floor. Discarded mandarins are visible in one of them.
The easiest way to reach Tsukiji is to take a metro. Tsukijishijō station (築地市場駅) on Toei Ōedo line (都営地下鉄大江戸線) is the nearest one.