Ablutions

You have to pick up the note on the decontamination arch near the entrance of The Nucleus and read it to get the objective added. Talk to Sister Mai and ask her if she needs help with anything. She'll mention about recovering a pump regulator from the Vim Pop factory. If you agree to recover it for her, this sidequest will start (Longfellow will dislike this decision)

Head to the Vim! Pop Factory to the southeast of the island. This place is crawling with Super Mutants so you have to be cautious and make the necessary preparations. Refer to this location’s page for more information about the loot and where to find the pump regulator.

After retrieving the pump regulator, talk to Mai again and she’ll ask if you’re willing to do the honor of installing the part to the modified decontamination arch. You can demand for more caps through a speech check and you’ll also receive the Radical Conversion weapon.

Find the pump at the bottom of the drained submarine pen then examine it. You can install the regulator or if your INT is 7 above, you can reverse Mai’s bypass and fix the decontamination system. One you’ve installed the regulator or tampered with it, go back up and test the arch. Once done, the quest will be complete.