How many gallons of fuel did I start with and end up with

I think you will be looking at about 500 gallons.
598.4 US gallon.
498.3 UK Imperial gallon.

You can convert pipe size to gallons per minute of flow by calculating the cross-sectional area of the pipe and making some reasonable assumptions about pipe volume and the rate of flow. Pipe sizing is measured by the internal diameter of the pipe, not the overall outside diameter. Once determined, the overall volume can be calculated. Pipe flow is described in gallons per minute. Shorter lengths of pipe will have a greater flow than a longer length of the same diameter. This is caused by internal resistance of the pipe itself. By the same reasoning a larger diameter pipe will have a greater flow or GPM than a smaller pipe at the same pressure or flow rate. Pressure is described as pounds per square inch. The square-inch measurement is determined by the area of the pipe. The pounds are the amount of force that is placed on the liquid to push it through the enclosed space.With that background, you can estimate the flow based on the pipe size.
Find the cross-section area of the pipe. Area is equal to pi times the radius squared or a = 3.14 x r2. A two-inch diameter pipe would have a cross-section area of 3.14 x 12 or 3.14 square inches.
Understand that water has a certain pressure associated with the height of that water. One pound of water pressure, or 1 PSI, is equal to 2.31 feet of elevation in height. In other words, a 1-inch column or pipe of water that is 2.31 feet high will have a pressure of 1 PSI. The overall height -- not volume -- of the pipe corresponds to the pressure. A 6-inch diameter pipe that is 2.31 feet high will only have 1 PSI.
Find the volume of the 2-inch diameter pipe in Step 1 that has a length of 10 feet. Ten feet is equal to 120 inches. Multiply 3.14 square inches, the cross sectional area, times the length. The volume of the pipe is equal to 376.8 cubic inches of volume.
Convert cubic inches into cubic feet. One cubic foot equals 1,728 cubic inches. Divide 376.8 cubic inches by 1,728 cubic inches per cubic foot and the answer is .218 cubic feet. This means that the 2-inch diameter pipe that is 10 feet long has an internal volume of .218 cubic feet.
Calculate the amount of water that can be contained in the section of pipe at any given time. One cubic foot of water is equal to 7.48 gallons. Multiply 7.48 gallons by .218 cubic feet and the amount of water in the pipe is equal to 1.63 gallons.
Find the GPM if the flow of water is one foot per second. Multiply the one-foot per second flow by 60 seconds per minute and the flow is now 60 feet per minute. In other words the water will flow through the 10-foot pipe six full volumes for every minute. Since the piping contains 1.63 gallons per 10 feet of pipe, multiply 1.63 by six and the final GPM is equal to 9.78 GPM of water flow from the 2-inch diameter pipe.

Formula For Average Gallons In Rectangle, Square Or Freeform Pools:
Length x Width x Average Depth x 7.5 = Total gallons
Formula For Average Gallons In Circular Pools:
Diameter x Diameter x Average Depth x 5.9 = Total gallons
Formula For Average Gallons In Oval Pools:
Length x Width x Average Depth x 5.9 = Total gallons
Formula For Average Depth Of Pools With Slopes:
Shallow End Depth + Deep End Depth Divided by 2 = Average Depth

That would depend on the length of the tank. A very long tank won't have a large diameter, while a short tank will.

With its generous 190- gallon fuel capacity and twin outboard power by Mercury Marine, the 2502 is rigged to make short work of the long run offshore.

Figure it out this way, the formula for a round vessel is:
(The formula is for "Feet" so make the proper conversion 1st)
you also need to know that there are 7.5 gallons in a cubic foot

Pi x r2 x depth = cubic feet x 7.5 = total gallons
3.14 x (65" = 5.42' diameter, 2.71' = radius {squared} x 2.71 = 7.34 x 2.75 x 7.5 = 475.36 Gallons

18,600 gallons (length x width x depthx 7.51 =gallons)

72 x 29 x 24 = 50,112 cubic inches / 1728* = 29 cubic feet. There are 7.48 gallons per cubic foot, so the tank is actually 216.92 gallons, assuming the dimensions given are inside measurements. I hope you have a strong stand and floor because the water alone weighs 1735.36 pounds (8 pounds per gallon).

*12 x 12 x 12 = 1728 (cubic inches to cubic feet conversion)

The tube in the tank is the fuel pickup line and goes directly to the carburetor. You will need to get NEW fuel lines. Fish or shake the old parts out of the fuel tank after draining. Inside the tank will be a small length of smaller diameter fuel line that connects to the small fuel filter and there will be a small nylon line connector that is plugged into the end of the larger diameter fuel line which is the fuel return line from the primer bulb back to the fuel tank. That line ends just inside the fuel tank and is held there by the small nylon line connector. The other line (smaller diameter) needs some length inside the tank so it can flop around as you move the machine enabling it to always pick up fuel. 6" or so is about right from the hole in the bottom (or top) of the tank to the fuel filter. Buy long enough lengths of fuel line that they can be inserted into the tank and pulled thru the fill cap area and then have the parts put back on them and then cut to the correct length from the fuel tank to the carburetor and/or primer bulb. Buy about 1 foot of each size line needed. Small engine repair shops have it and sell it..not expensive.

Three basic methods:
1.Run power to the garage and reclocate the compressor there.
2.Use 3/4" steel or copper pipe run under ground to move the air without loosing as much pressure.
**3. Keep doing what you are doing but...add a portable air tank at the end of the line. I would suggest 11 gallon and add a large diameter 1/2" or 3/4" ID hose that is only 12 feet off of that to reduce the loss of pressure. I even ran a 100 pound propane construction size tank (after cleaning it and refitting it with large diameter pipe) Use a "cross" piple to get air into and out of the tank. Just remove whatever the portable tank has on it and create your own setup. This really works well.