You did not need to know the amount of water originally in the overflow container because it could be easily calculated with the existing information.
To find the volume of an object, we use an overflow cylinder as it gives a measure of the volume of the object by displacing an equal amount of water into the beaker.
When a heavy rainstorm results in water greater than 2 inches, the water flows over the top of the inner container and into the overflow can, which is 4 inches taller than the inner container. The observer measures and records the amount of rain in the inner container and empties the inner container. Then, the observer carefully pours the water from the overflow can into the inner container, measures it and records it. The observer adds the two recorded totals together to obtain a final amount of rainfall.
The density of the rock can be directly determined when the rock is placed in an overflow container. By measuring the amount of water displaced by the rock, its volume can be calculated, and then by dividing the mass of the rock by its volume, the density can be determined.
Fill a container with water. Carefull put the object into the container and collect the overflow of water. Measure the water displaced See "Eureka"
if your water/antifreeze gets to hot it pushes out the over flow tube into the overflow container, as it cools down it will suck it out of the overflow and back into the radiator.
fill thru the overflow container
Water molecules are smaller than alcohol ones. Water ones can fit between alcohol ones. Fill a container with pure alcohol to the top and add water. A certain amount will go into the container and not cause it to overflow.
1/2 distilled water 1/2 antifreeze to the full line in the overflow container.
Take a container with a rather precise scale and measure it. Place the ring inside and measure it again. The amount the water goes up is the volume of the ring. Or you could fill a container to the brim with water, with a collecting dish underneath. Put the ring in the container, which would cause some of the water to overflow. The volume of water that left the container is the volume of the ring. Or you could take a clay mold and make a mold of the ring, fill that with water and measure how much water it takes to fill the 3D mold.
Fill the bath right up to the overflow. Rig the overflow to a large container. Put me in the bath, so I float. Catch all the water that comes out of the over flow. Weigh the water on the bathroom scales. That's my weight.
If there is no overflow of water, then the container's over-all weight goes up by the weight of the fish. The weight of the water itself doesn't change.
Immerse the object in water and measure the volume of water that is displaced. One way would be to fill a container, large enough to hold the object, with water until it is just about to overflow. The container and water would need to be inside another container that could capture the displaced water. Submerge the object in the water and then measure the volume (or weight) of the water that overflows