I know there are a LOT of older threads on using Foodsavers with canning jars. I have read many of them, but I haven't found any addressing the problem I'm having:

My Foodsaver seems to form the vacuum on the lid 100% of the time. It works perfectly ... for a while. But eventually many of the vacuum seals have failed (with the distinctive POP of the lid, if I'm around to hear it).

I did one jar of sugar several weeks ago. I don't know when the vacuum failed, but I saw yesterday that it had.

Yesterday I did over two dozen jars of powdered milk. Every one seemed to be perfect, but even as I was finishing up the last few, I started hearing the dreaded pops of seals failing on the first ones I did. Overnight another half dozen or more had failed.

I can understand the problem with the powdered milk, as when I finished each one and removed the attachment, there was evidence that some powder had come up between the lid and jar top while the vacuum was being created. And when I open one of the failed jars, I can see some powder did get on the seal portion of the lid. So I'm thinking I need to put the powder into a bag first, and then put the bag in the jar.

But the sugar did not have this problem. The seal on the lid looked fine, so I don't know why it would fail like that.

The lids (and jars) for the powdered milk were all new, but the sugar jar and lid was older. (The lid seemed fine, though there is a very small dent on a portion of it.) They are Bell brand jars.

I do put on the screw portion of the lid after I'm done. I know that isn't necessary, but can it hurt to do so?

Any suggestions or info would be appreciated. I have yet to try soaking the new lids in hot water as I've read here, but I do intend to try that today.