The same as always, *unused* blood test tubes! They were surplus to requirements after one of our studies finished.
For those that haven't seen them before, they are used as leakproof containers for shipping blood samples to labs on the Continent (so if they had been used, they would no longer be in the country!). All the contents have been removed and they're not contaminated - they haven't been used.
We get sent dozens of kits for our research studies and there are always some left over at the end. They can't be used in the hospital so to save the NHS from paying for them to be disposed, we recycle them as caches!
- Nik