This weapon seems like a great choice for the upcoming pyro update because I think it could add a new dimension to the class or at least, bring new concepts to this game.

First off, the Fumigator would have stats identical to stock and use a new damage type: poison. Poison damage would be structured exactly like afterburn damage (6 dps), only that water, milk, jarate and airblast wouldn't shorten it's effects. The only cures would be either picking up a health kit or having a medic heal you. The damage from poison would also not be effected by fire-related resistances, since it's not technically fire.

The only stats on it would be this:

+not a fire based weapon
and
-not a fire based weapon

The plus obviously is there because of how it ignores the resistances(shields, MVM)and counters (milk, karate) of fire damage present in the game.

The minus, however is that it can't pair with any fire-related weapon, such as the flare gun, axtinguisher, sun on a stick, etc. This makes the pyro a more technical class, aiming to expose the cracks in the enemy's strategies rather than rely on a gimmicky weapon combo to even compete with the killing power of other classes. This weapon would also encourage use of alternative secondary and melee choices due to incompatibility.