Open the Shortcuts app and tap +
Shortcuts comes with every iPhone. If you deleted it, download it again from the App Store for free.
Add "Set Volume" at 100%
Tap Add Action, search for Set Volume and set it to 100%. The tone works best at full volume.
Add "Open URLs"
Search for Open URLs and type waterejectphone.com as the address. The shortcut now opens this tool in Safari.
Name it "Water Eject"
Tap the name at the top and call it Water Eject. Siri uses this name as the voice command. Tap Done.
Run it
Say "Hey Siri, Water Eject", or tap the shortcut. When the page opens, press Eject water. To put it on your Home Screen, touch and hold the shortcut, tap Share, then Add to Home Screen.
This shortcut uses only Apple's own actions, so you don't need to install anything from a third-party link. Searching for a "water Siri eject shortcut" leads to the same idea: a shortcut you start with your voice that plays a low tone.