2% salt brine in water that’s of the total weight of beans plus water. What’s I do is:

• Soak dry beans in fresh water for at least 8 hours or overnight.
• Drain off the excess water from the hydrated beans.
• Get a jar and tare the weight on a scale.
• Add the beans and cover by about 1 - 2 inches of water.
• You want to get the weight of the beans plus the water. So I tare the jar on the scale and then add the beans and water and weight again. You could also write down the jar weight and then subtract that weight from the total.
• You then multiply the weight of the beans and water by 0.02 to get the weight of salt you add. So let’s say you have 1500 grams of beans and 1000 grams of water you have 2500 total weight. 0.02 of that is 50 grams of salt. Weight it out then add to the jar with beans and water. Put a lid on and shake it a bit to dissolve the salt. Then put on an air lock lid for the jar.
• You will want to put the jar somewhere out of the way. Beans don’t exactly smell the best when fermenting. Not necessarily “bad” but very unique and not exactly a pleasant smell either. But that’s the price of not having those gasses come out your bum later.

I use mason jars of varying size. Some store bought lids with air locks. Some I have made myself for odd shaped jars with lids not commercially made with air lock options. Will try and get a few pics.