Any container of any shape with a volume of 6.6841 cubic feet or more will do the job.
For a rectangular container, multiply the (length) x (width) x (height). If the result
is 6.6841 or more in feet, (11,550 or more in inches), you're in business.
A million gallons is really a lot; I would say, an extra-large swimming pool could be large enough.
If you mean inches, it can hold up to 6,739.95 gallons. If you mean feet, it can hold up to 11,646,630.24 gallons.
A 35,200 cubic foot container can hold up to 263,314.29 gallons.
My swimming pool holds 1250 gallons. It is 12 feet diameter and 3 feet deep.
24,685.7 gallons.
This container could hold up to 3,949.71 US gallons of water.
19.64 US gallons.
10.38961 gallons (rounded)
Well, as an example, a 70-cubic meter container could hold up to about 18,500 gallons of water.
your ugly cats face
About 47.6 gallons
Figure the volume in cubic inches and divide by 277.4 to get the number of gallons the container will hold. This is A close approximate formular. Convert the gallons to pints or less if it is a small container.