The Nalgene Wide Mouth Rectangular Bottle (64-Ounce) work for me, and I don't worry about confusing them with my 32 oz cylindrical Nalgene drinking water bottles.
For women, add something like the Lady J.
For anyone who might consider it, I'm able to use the wide-mouth Nalgene bottle while on my side, while my girlfriend needs to be more vertical. We don't have any kids, but, it isn't tough to stay covered up while urinating in to a wide-mouth Nalgene bottle, with the right sleeping gear. Warmer that way too, especially at -20 F.
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As a side note, we’d also come to the realization that if you’re traveling with another person in a small camper in a third world country and can’t go to the bathroom in front of them…you probably have a much bigger problem." from Gary Wescott:
Overland Journal's Chris Collard interviews one of the most well-traveled duos in overlanding.
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