How can I improve sealing of bags for sous vide?
Edge sealing vacuum machines like yours are not really designed to cope with liquids, either water or oil. In fact, you can permanently damage your device if those liquids get sucked into the pump. There are ways around this, one is to feeze any liquids you wish to add to the vacuum bag or if your model supports it you can follow the advice from eGullet here:

http://forums.egullet.org/topic/144300-sous-vide-recipes-techniques-equipment-2011/page-2#entry1779665


  Sealing liquids is possible with clamp-type machines. Other members stated this long ago. I did not manage to do so at first, but now I have learned the trick. It does not work with fully-automated machines that have no "seal"-button and no external vacuum-port.
  Place the machine in a way that the bag can hang down vertically. Place the adapter on the external vacuum-port (without the tubing). When you start vacuuming, air will enter through the external vacuum-port, so almost no vacuum is built up. By closing the port with your finger, vacuum will rise and so will the liquid in the bag. Before the liquid approaches the sealing bar, reduce vacuum by lifting your finger, and press the seal button. Make a second and eventually third seal in case the first one should not be perfectly tight.