We entomb it in massive concrete caskets with a volume up to 5 000m², lined with plastic to prevent leaking, and when it’s full we cap it and bury it under 3 meters of dirt.
It used to be around 1-2m wide clay bowls that were filled halfway and there was a variety of methods to cap it off. The reason for famines and things like the black death were people who just buried it in dirt, the cursed crap leeched out.
That’s not even in the scene.
https://www.youtube.com/watch?v=GX-m7UsCp3I
Here’s what Walter actually says: