What is the best / easiest / cheapest way to measure large quantities of wvo when filling up your processor?

What do you consider large quantities?

Brian,
If I remember correctly you were building a 50 gallon appleseed?
The way that we do it is that we calibrated a "dipstick" for our filter/dewater drum. This makes it very easy to determine how much oil you are using.
Where in NY are you? I'm not sure if there is a town called Hudson Valley or not?
DD

1) calculate the gallons per inch of depth(inside diameter squared, x Pi /4 /231, or inside diameter squared/294.1 = gallons per inch).

2) connect a clear hose to a low point on the tank, hold it against the side so show the depth of liquid inside. (this is almost a site glass)

I consider large quantities to be anywhere from 15 to 40 gallons of oil (factoring in room for methoxide). And yes, Don, I am building a 50 gallon processor (though I have an 80 gallon heater in reserve, just in case!).

I didn't put my town in the profile because I'm trying to maintain a little bit of 'net anonymity. I'm in the Middletown, NY area.

I like the idea of the drum dipstick. I have a pair of 30 gallon plastic drums, and have planned to make 25-gallon batches, so it should be pretty straightforward to do that myself.