I have two 699s and both are among my favorite Chinese pens. No leaking… You may have gotten a defective pen, unfortunately. Are you storing it with the blind cap screwed closed the whole way? If the blind cap is fully closed, the pen shouldn’t be leaking at all…
The burping can happen with vac fillers as your hand’s warmth causes air in the barrel to expand, pushing out the ink. Filling the pen up more fully may help - less air to expand. Are you writing with the blind cap open? This may help as there won’t be a sealed off barrel in which the air can expand.