101Leafy researched the game with the Hilltop Works fan translation patch, English translation by Cargodin
Gargle Water is item 77 of the game's item table, in the Items group. The script names it on disc 2.
Lines of the script that name it, each with a link to its place in the script.
You've got quite the reputation. Us locals have to be cautious, so it takes a second for us to loosen up. ... Here. This will open the hutongs. Use it at the Victoria Mansions door. This is gargle water. Just gargle it. ... Yeah, just like that.
The Ghostmaster is somewhere deep in Victoria Mansions. I think they're the cause of all this.
どうやら信用されたみたいだな。私たちは、用心深く生きることに馴れているからね。これを使うと、胡同への扉は開く。維多利亜大廈（ビクトリアマンション）の扉だよ。ほら、うがい水だ。うがい…だろ…それでいいんだ。
物の怪使いは、維多利亜大廈の奥にいるんだよ。私は、そいつが元凶だと思うね。
Gargle Water acquired.
「うがい水」を入手しました。
Okay. If you believe in us, we'll believe in you too... Four structures make up our hutongs. The only structure we can open up is called "Victoria Mansions". There's a Ghostmaster in there. That Ghostmaster is the ringleader of the guilü swarm on the inside.
Give the Ghostmaster the boot, and the hutong's malice should follow.
To get into Victoria Mansions, you'll need some gargle water. The kind you rinse your mouth with.
ようし…俺たちもあんたを信じる、あんたも俺たちを信じると。胡同には４棟の建物があるんだ。俺たちが開けてやれるのは維多利亜大廈（ビクトリアマンション）だけだ。その奥に物の怪使いが潜んでいて、そいつのせいで鬼律がうようよしてるんだ。
物の怪使いを封じ込めれば、胡同の邪気はなくなるはずだ。
維多利亜大廈に入るには、うがい水があればいい…歯を抜いたときに使う水だよ。
Gargle water, understand? ... Seriously? Come onnn!
Haven't you ever gargled water at the dentist's office after he plucked a few teeth?
... Whatever. You'll need some to get inside Victoria Mansions.
うがい水…わかるだろ、うがいの水だ。…違うか…
歯を抜いたときに口をゆすぐ水…うがいじゃないのか？
とにかく、胡同に入るには、その水がいるんだよ。
Used Gargle Water.
「うがい水」を使用しました。
Item table: Xiaohei's Photograph Gargle Water Victoria Mansions Key
English translations by Cargodin for Hilltop Works Fan Translation Patch: https://www.patreon.com/hilltopworks/posts/kowloons-gate-160555525?collection=18503