You'll need a long cycle, longer than is usually found on a washing machine, to give the dye plenty of time to react with the fabric. You should stay near the machine and reset it before it begins to drain at the end of a wash cycle. If you want to walk away from the machine, you should wear a timer (clipped to your clothing, or on a cord around your neck), to remind you to return before the end of the cycle; otherwise, you may find yourself wasting dye and auxiliary chemicals, letting them run down the drain before you are done with them. Some top-loading washing machines will agitate but not drain if the lid is left open, in which case this is a very easy way to avoid problems.