If you followed the Pf tek, then you used Vermiculite and BRF, yes? Well basically, dunking is the process to rehydrate your cakes. Since mushrooms are 90% water, they typically grow bigger and grow more of them per flush. To dunk a cake you basically find a tupperware with lid and fill it with a capful of peroxide and water. Place your cake in the water so it is fully submerged and put in the fridge for no more than 48 hours. After the cake has been in there long enough (24 hours is a good range), you roll the cake in damp vermiculite and place in the fruiting chamber.
So my process has become, immediately after birthing I dunk the cake for 24 hours then place in the fruiting chamber. After most of the pins have become mushrooms and the cake is producing pins slower, I re-dunk the cake for 12 hours. You can repeat this up to about 4-5 times before all the nutrients in the cake are spent. But the beauty of this process is one cake now has the life of 3 or 4 cakes and can yield more mushrooms.
My first cake I got 3.5g off of. After dunking, the second flush again, 3.5g. So that's 7g off one cake so far with more mushroom still waiting to grow! Plus this cake still has at least 1 more flush in it, which could get me another 2-3g. That's almost 13g for one 1/2 pint cake.
Once you've picked all the mature mushrooms, that is a flush. Then, just dunk and roll and your good to go for round 2.