You can start this quest after speaking to Sister Mai at The Nucleus. Your next stop is the Vim! Pop Factory.
Make your way through the factory but be cautious as the entire building is crawling with Super Mutants and Mutant Hounds. There's a Vim branded suit of T-51 Power Armor on the upper level of the factory floor along the catwalk. Check the Vim Ambassador terminal in the same room to acquire Vim paint job Power Armor schematics and learn more about the Vim Ambassador Program.
Unlock the loading dock doors on the lowest level of the factory floor to meet Grun.
The industrial-strength pump regulator you're searching for is on a desk overlooking the mixing room. Return the regulator to Sister Mai and she will reward you with Radical Conversion.
Mai will give you the honors of adding the regular to the decontamination system in the bottom of the bay, near the rear of the vessel. Once there, you have the option to install the regular and let Mai's bypass do it's job of spraying irradiated water or to reverse the bypass and to fix the decontamination system so that the arches cleanse radiation instead.
Whatever option you choose, you will have to test the decontamination system to finish the quest. If you choose to undo Mai's bypass, you have a theoretical way to rid yourself of rads.