I had the same issue and got a reply from Jeff (the eBay seller), who's very courteous and helpful.
"You will get powder in the tank occasionally when you charge the filter. It is not great for the fish, but it will not harm them.
I have used diatom filters for years. Apply some silicone lubricant to the jar o-ring the next time you change powder.
That should reduce the bubbles, or make sure your suction hose connections are tight."
I applied some silicone lubricant around the o-ring but I'm still seeing bubbles every few minutes.
The bubbles don't bother me since it's in the sump and the baffles reduce them dramatically by the time it reaches the return pump.
I have tried the same and have been unable to eradicate the bubbles. What I did was place a ball valve on the output end and when throttled down a 1/4 turn, the bubbles all but go away. I also use it in the sump, so whatever few bubbles get in are addressed by the baffles.
Good luck!