It will help to find a container to hold it.
The proper container is described in the spell book from the book shop.
You need to get a teacup from the Garden (next to the swamp). It will appear on a chair as soon as you are ready to use it.
Now, try to fill the teacup with swamp ooze.
You need to take advantage of the sibling rivalry between the bump-on-a-log and the stick-in-the-mud.