I find the easiest way to remove poisons if I no longer want them on my weapons is to do the following:
1) Find a friend who you enjoy playing with
2) After some time getting close to this person, exchange account info
3) Randomly call his mother a cum-guzzling whore
4) Wait for friend to log onto your account and delete your items, including weapons
5) Petition TwinStar to restore hacked account.
6) Weapons are usually restored without poisons.
7) Befriend new player for future depoisonings.