Place grapes (removed from stems) into your large stock pot. The amount you use is flexible, but stay below 2/3 the height of your pot.
Crush the grapes using a potato masher or similar tool.
Add just enough water to the stock pot to cover the crushed grapes.
Bring the grapes and water to a boil over medium-high heat.
Reduce heat to low and simmer grapes for 30 minutes.
Place the strainer, lined with cheesecloth, into another large bowl or second large stock pot.
Pour the grapes and water into the strainer and allow juice to flow into the other pot/bowl.
Place the pot/bowl and strainer full of grape pulp into the fridge to continue draining for 24-48 hours.
Remove and discard (compost!) the grape pulp.
Carefully pour the grape juice back into the first stock pot (cleaned). Stop when you reach the bottom of the juice and any sediment that has gathered (you are basically decanting the juice here).
Enjoy! (or preserve for later) Note: If your grape juice turns out thicker than you like, simply add more water when serving, or mix with seltzer for an awesome homemade soda!