The only things you need are bleach and water! (And your pumpkins, of course...)
Follow this formula: 1 cup of bleach + 3 cups of water.
You do not have to soak the pumpkins; simply use a cloth or brush to wash them gently in the bleach and water solution.
Place your fresh-washed pumpkins on an old towel to dry.
This step doesn't even have to be done immediately after washing; you can do it at any point. I waited a day after washing my pumpkins because we were experiencing high humidity outside, and I wanted the weather to be optimal for the sealer to dry well. Either way, it will add a nice shine to your pumpkins and help them last longer.