Fire and Frost ...Waterworks Rin

Both feeding from a single tank, this has the potential to last longer. Have a sensor that causes a pump to activate, so the liquid goes out of their tube, and back into the main.

Now what should trigger the sensor? Lust? So as long as they press their crotch against the sensor they are aroused, but if they orgasm the water flows normally. So they just have to ride their lust until Rin gets tired of the show, and swaps the setting.

Now they have to orgasm over and over to keep the water pumped out. Hope they have a healthy appetite for sex, they'll be needing it.