Back flooding is an important procedure screen printers use on-press to keep the stencil printing well. This is a very simple way of keeping the ink left in the stencil wet between prints. That being said, it is an easy thing to forget to do. Back flooding occurs when you follow up a print by flooding ink back into the stencil with the squeegee in order to pull the shirt off the press, load new shirts, or print other colors.
Between printing each screen, make sure the stencil mesh is completely flooded and filled with ink. You’ll want to keep enough ink on the screen to back flood the stencil with a nice thick coat of ink.
Thinner inks should run less when spread out, which helps control the ink on the screen when it is in the up position. Be careful not to use too much pressure on the back flood. You don’t want to extrude the ink through the stencil; you simply want to cover it with the ink. It should naturally fill in the mesh without much pressure from the squeegee. The thinner the ink is, the less pressure you may need to do the back flood.
Source: Jonathan Monaco, Catspit Productions