Cooking spaghetti in multiple pots and preparing the noodles before the event help make the process easier when making spaghetti for a crowd. If available, use two to four pots of boiling water to cook as much spaghetti as is needed. Only cook the pasta to al dente or even a little under al dente. Then, when the spaghetti is reheated later, it doesn't become overcooked.
After cooking the spaghetti to al dente, immediately drain the noodles, and toss them with butter or oil until they've all been coated to prevent sticking. Put the spaghetti in the refrigerator in small containers, as small amounts of pasta cools more quickly and therefore not continue cooking. Immediately before the meal or event, reheat the spaghetti by placing it in boiling water for a minute or two.
When cooking spaghetti for a crowd, determine the appropriate total amount of pasta by multiplying the total number of guests by 2 ounces of dry spaghetti. When cooking, use roughly 5 quarts of water per pound of dry spaghetti.
Don't rinse the spaghetti after it's cooked. Rinsing cooked pasta can strip away essential starches. Also, avoid adding oil to the water when boiling spaghetti, as this makes the noodles too slippery for sauce to stick.