[hannah-]

Wear the same pair of underwear all week. Cum as much as you want, but each time you cum into this pair of underwear. After 1 week, put it in a zip-lock bag and cum once more just before sealing it.

Then take a fresh pair of undies and pee on it, make it thoroughly soaked. Place it in a zip lock bag as well. Put both bags out in the hot sun for an hour or two. If there is no sun, wait for another day.

Then blindfold yourself, wear thick gloves and switch around both bags until you lose track which one contains which undies. Pick one at random. That's the pair you have to pull over your head. Enjoy the smell. (Oh and tape your mouth shut, only breathe through the nose.)

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fyi, I was made to post here (but this does not mean the next person should go easy on me).