What's the trick to seal sous vide foil if liquid contained
I would say that having lots of liquid makes your life easier, not more difficult, because you don't need the vacuum at all. 

The purpose of the vacuum is to have heat conduction take place properly. If you were to put a piece of dry food in a plastic bag and close that, the air trapped in the bag would act as an insulator, preventing from the water bath to heat the food. 

The good thing about marinades and other liquids used in cooking is that they are great heat conductors. So if you have a bag full of liquid, with pieces of solid food swimming in it, the sous vide process works as intended, without any vacuum. 

The most practically convenient way to go about it is to use ziplock bags without a vacuum device. You place your food-with-liquid in the bag, submerge most of the bag, and manually press out the air, then seal by hand. A few air bubbles will be left inside, but they're not a problem. 

From there, you can proceed the same way as with a heat-sealed voided bag.