Remove the packing nut and rubber gasket or washer inside.
From the dispatch.com
Unscrew the packing nut counterclockwise.
From the thestate.com
I can loosen the packing nut, hoping that loosens the main valve so it can be turned off, but then there is sometimes a threaded part under it that comes loose and leaks.
From the dailyherald.com
Wherein a nut ban in an elementary school makes packing a school lunch that much harder.
From the eatocracy.cnn.com
Some schools are requiring that no nuts be allowed on their campus at all, which means parents must also follow the nut-free policy when packing lunches and snacks.