I'm american, so i've only heard myths, and legends about the fabled adult sized baby diapers. I've seen pictures. They more than likely can hold around 2000mL, if not more.
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I haven't heard much about rearz on use. I've seen people on youtube review the rearz pink princess diapers who've said that they've worn it for 12+ hours without problems. they also lock scent, and are advertised as being able to hold 5000mL! I've heard they are extremely crinkly, however.