I wear basic Fruit of the Loom boxer-briefs that fit snugly yet comfortably, and I sewed the front opening closed. The back opening I sewed 2/3rds closed, leaving just enough room in the middle of the fly to put my packer inside the pouch my sewing made, and adjust it so it fits nicely against my body. That way, I have no fear of it slipping out the front hole while walking or running. (I've heard of that happening!)
As for cleaning it, since its not directly in contact with my skin, I usually feel there's no need to wash it very often. But whenever I do wash my packer, I use warm water, mild hand soap, dry it off, let it air dry and lightly apply corn starch in the ziplock baggie I keep it in. Make sure to get the kind of cornstarch from the baby isle, NOT the food-grade stuff!
I hear that talcum powder is somehow unsafe, but I don't know why. Maybe it reacts with the silicon or something. Idunno.
Either way, good luck and enjoy your packer!
Ryuichi
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