Something seems strange, from the sources I've found, 4 cups (1 quart) of liquid whole eggs weighs about 34.286 ounces or 2 pounds 2 1/4 ounces. Therefore, 5 gallons (20 quarts) would weigh about 42 pounds 13 3/4 ounces, not 20 pounds as you indicate, maybe it is 20 kilograms? The weight of egg whites seems very close.

Total volume = V

Volume of liquid eggs = L

Volume of egg white = W

If the recipe calls for 30% of the TOTAL VOLUME to be egg whites, then V = L + W and %W =( W/V)*100 = (W/(L+W))*100 = 30%

So, dividing both sides by 100 : W/(L+W) = 0.3

Multiplying both sides by (L+W): W=0.3(L+W) = 0.3L+0.3W

Subtracting 0.3W from both sides : W-0.3W = 0.3L or 0.7W=0.3L

Dividing both sides by 0.3: 0.7W/0.3=0.3L/0.3 or 2.3333W=L

Dividing both sides by 2.3333: W = 0.42857755L

What the h3ll does this mean? For every 5 gallon (20 quarts) bag of liquid eggs, use 8.57155 quarts (8 quarts, 18.29 ounces) of egg whites or 8 quarts + 2 cups + 2 ounces + 1 teaspoon + 3/4 teaspoon of egg whites.

8.57155 quarts of egg whites divided by the total volume of 28.57155 quarts = 0.30 = 30%

I'd probably use 8 1/2 quarts of whites per 5 gallons of liquid eggs.

I'd certainly check the weight of 5 gallons of liquid eggs before proceeding.