I think a better adv basilisk improvement would be if the fart hangs in the air for a about 5 seconds before dissipating, and walking through the cloud triggers its effects. Of course, the basi would only be able to fart once every 10 seconds or so. (maybe as fast as every 6 or 8 seconds) The cloud would also take a second or so to become "active"; it wouldn't be instant like it is now.
What this would allow, is for basilisks to help teammates escape when low on HP. Tyrant's running away with 100 HP? Spray a fart behind him, so that any humans that follow have to go through it and get disoriented, dramitcally improving the chance of survival of that Tyrant.
Also, I think the fart effects have to be rethought. As is, the poison makes you tipsy. Now, I don't know what kind of effects are possible in Tremulous, but large amounts of motion blur would be a much better effect. Instead of just screwing with your crosshair, instead your vision would be so blurry you'd barely be able to SEE the aliens. Basically, a poison that affects your vision in order to decrease your accuracy, instead of simply decreasing your accuracy.
Alternately, the poison cloud should deal poison damage the same was a boosted attack does, in addition to the disorientation.