How do I remove poison?
Solution 1:
Red potions and Dispel Magic can apparently cure poison.
If I remember correctly, you can also awaken Lord British (using Dispel Magic, Mass Awaken, or a blue potion?) in the middle of the night and then ask him for healing.
Solution 2:
Apparently, "Dispel Magic" cures poison:
http://www.gameboomers.com/wtcheats/pcUu/Ultima6sh.htm