Clentaminator

The Clentaminator can be bought from the Steampunker. It is used to create/destroy biomes and it uses Solution as ammo. It has the same firing pattern as the Flamethrower, and is not stopped by any block. It also has a longer range than the flamethrower. Green, Blue, Red, and Purple Solution can be bought from the Steampunker, while the Dark Blue Solution can be bought from the Truffle. The only time you can buy Purple Solution and Red Solution is during a Blood Moon, which spreads Corruption and Crimson. It's the fastest way of spreading the Hallow, Corruption, Crimson, Forest, and Mushrooms.

Tips

 * Do not move your cursor too quickly while using the Clentaminator. Doing so will not get everywhere you are trying to convert most of the time. Move it slowly across the screen.
 * Make a circle with your mouse slowly and stop when you reach back to where you started. You can go a little bit beyond the starting point to make sure you got everywhere. This should convert all blocks visible on your screen. It is very useful for fighting The Corruption and Crimson.
 * If you have an Ice Rod or any other item that emits light that can pass through blocks, it should help you find areas to convert.
 * The Clentaminator is affected by armor sets that reduce ammo usage and as Solution is expensive, this is highly recommended. A set of Adamantite armor (with the Mask) or Hallowed armor (with the Helmet) will reduce Solution consumption by about 25%. While wearing Chlorophyte Helmet and Shroomite Breastplate, Solution consumption will be reduced by about 40% (losing any armor set bonuses).
 * The Clentaminator has a range of about 61 blocks horizontally, therefore you can cleanse or contaminate your entire world by making Hellevators about every 120 blocks and while slowly descending every one of them spray on both sides.