A dry pail is an empty basket used to store dirty nappies until wash day. The ideal dry pail has holes in the sides and allows for lots of airflow. This minimises the formation of ammonia, by evaporating the water from urine.
Decades ago wet pailing was the most common method of dirty nappy storage. This is no longer a suitable or needed option. Napisan previously contained sodium hypochlorite (the active ingredient in bleach which sanitises), it no longer does, so the modern Napisan/Vanish does not sanitise. Wet pailing poses a drowning risk, creates a perfect breeding ground for bacteria to flourish, constant soaking of nappies degrades them prematurely and is more labour intensive.
Wet bags are water resistant bags made of PUL, which can be used for storing soiled nappies while out. They are also useful for wet swim wear and clothing.