Squirtbottle

The Squirtbottle is a type of Oak Item. When equipped, it increases the chance of mutations occurring in the Farm. Unlike most other Oak Items, it is not unlocked by capturing unique Pokémon and instead can be bought from the Johto Berry Master in Goldenrod City. It also requires Farming Points to upgrade instead of Pokédollars.

Leveling Strategies
There are a few strategies on how to level up the Squirtbottle based on which berries you have unlocked.

Occa/Kebia Planting Formation
If you want to be able to gain experience more passively, then the best strategy is with Occa and Kebia berries. Colbur works for this as well, but takes longer enough to grow that is isn't as useful. This strategy will likely let you level up your Squirtbottle from 0 to 5 without having to set it up again unless you get unlucky with a full takeover. Note: When using this strategy, make sure to plant the berries so that they finish at the same time to lower the chance of full takeover.

Sitrus/Kebia Planting Formation
If you only have Kebia berries and neither of the other two, you can use Kebia and Sitrus at the same time in the following formation: Note: This will need to be set up every 20 minutes since both berries take 10 minutes to ripen, but you don't need to check on it more often than that.

Persim Planting Formation
Another common strategy includes mutating Persim berries is you haven't unlocked Occa, Kabia, or Colbur yet. You can find the formation and timings on the Persim page. This is a very active strategy, so is not recommended unless it is your only option.