A few thoughts -

First is that, no offense, but it doesn't sound like you really know what your doing with your vape. You're running all over the dial and, assuming your DBV is like mine, you're operating at way to high of temps. The temp range on your DBV is 200-900F. On my unit "OFF" is at about 7 o'clock, and full power is at about 4 o'clock. Assuming the switch adjusts the temperature linearly, 12 o'clock should be somewhere in the neighborhood of 550F - still too hot for vaping weed. On my unit I usually set it at about 10:30-11:00.

Second, make sure you're warming your unit up properly before you try to use it. Turn it to full power for a few minutes to give it time for the glass to get hot, then turn it down to your desired temp.

Third, if you've got your temps right, MJ vape is almost invisible. You especially won't see it in the tubing when you take a hit. You *should* however be able to taste it and it will seem more "smokey" when you exhale.

Hope this helps. Gotta say I love my DBV to death. Sad to hear you're having so much trouble with yours.