One Man's Trash -

Wiki:

Operation Tamarisk was a Cold War-era operation run by the military intelligence services of the US, UK and France through their military liaison missions in East Germany, that gathered discarded paper, letters, and rubbish from Soviet trash bins and military maneuvers, including used toilet paper.

It involved starving the Soviets of toilet paper. This led them to use official documents as toilet paper. The US, UK and the French then used their spies to retrieve the documents as the paper was not soluble and was put into bins. The spies actually complained to their handlers that they had to go through the bins that contained fecal matter and even amputated limbs. When the spies told their handlers this, the handlers immediately asked them to bring back the limbs as well so they could study what type of shrapnel the Soviets were using.