When I was younger and emptying the bathwater after a long soak I use to stick my mickey in the plug hole
The suction was lovely and the water whirling around my knob was something else
Special towards the end when it was nearly empty it kinda sounded like the plug hole was gagging on my cock
Now I reckon I got this idea from previously trying the hoover maneuver
In fairness I stuck it inot anything I could at that age but whats the weirdest place you've stuck yours