The water pressure depends ONLY on the height, and the density of the liquid - not on the number of gallons. You basically calculate the weight of a vertical column of that height, and divide by the base area. The column can be of any cross section - for example a square centimeter, a square meter, or a square foot. (For water, the pressure is about 1 bar for every 10 meters.)
it only depends on pressure at which the water flows into the gallon
On the inner rim of your toilet where the water flushes out from the cistern, if these small holes are blocked it wont make the right angled pressure to flush a toilet
That depends on the surface area over which the weight of the gallon of water is distributed. Divide 8.34 pounds -- the weight of a gallon of water -- by the area, in square inches, the gallon is sitting upon. If the gallon of water is in a typical plastic jug that you buy at the grocery store, it's not creating much pressure at all -- only about 2.2 ounces per square inch.
A wooden rain cistern is constructed very similarly to that of a whiskey barrel. However, those of us that have the equipment and knowledge to build a rain cistern (if we wanted to) know that the cost of the materials for a wooden cistern let alone the time to build it would cost considerably more to construct than purchasing a plastic or concrete water cistern. So if you are asking your question for the purposes of cost of a cistern, plastic and/or concrete are the way to go.
Errrh, would it be a gallon of water?
Yes. However, if you were to pour a gallon of water into a bowl on Mars, the water would boil and quickly evaporate because of the very low pressure.
A day or 2 depending on the water pressure
It depends on the flow rate in the hose and that depends on the water pressure.
Which water tank, well water, cold storage or hot water heater tank.
L x W x D = Cubic Feet x 7.67 = Gallon 8' x 25' x 14' = 2800cf 2800cf x 7.67 = 21476 gal
A gallon is equivalent to 16 cups. Therefore, it would take 16 cups of water to fill a gallon bucket completely.
It is standing water (a pond or puddle for example) as distinct from running water (such as a stream or river). Water temporarily stored, such as in your cold water cistern in your house, would not be considered as standing water, for it is replenished frequently.