Answer:
Donor sperm is frozen into small containers and then stored in tanks in liquid nitrogen or liquid nitrogen vapour.
The containers may be screw-top plastic containers (vials), or plastic straws which are sealed at the ends. These containers might hold as little as 0.2 mL, or as much as 1 mL.
In comparison, a teaspoon holds 5 mL. A normal semen ejaculate is about 2 mL. A human uterus can only hold about 0.3 mL of liquid.