XKC-Y25-V non-contact liquid level sensor

Capacitive liquid-level switch that senses water through the wall of a non-metallic container. The V type has a high/low level output: with the black wire left floating, it goes high (to the supply voltage) when it detects liquid and low when it doesn't. It comes in V, NPN, PNP and RS485 versions, so on AliExpress pick the V option. DFRobot sells it as SEN0204, the Gravity non-contact liquid level sensor. DFRobot's wiki says the current V2.0 package is a Y25-V sensor plus an XKC-Y25-T12V adapter board and a 3-pin Gravity cable, which you don't need for this build. It is one sensor per pack, and DFRobot rates the wall at 0–13 mm.