First question: is there a good way to do this?

Now, here is the strange thing. After getting most of 2 bottles filled I brought it inside and put the top on one jar, then put the siphon top on the other. I needed to make supper, so went into the house and did that. I came back out to my shop and all the paint in the siphon jar had run out all over the bench!!

I mean ALL of it! It was a mess, to say the least. Now, I have theories about this, being that there was air in the paint and as it released into the jar it pushed the paint up the siphon tube and out of the jar.

Anyone have any other ideas? It started doing it when I put the siphon cover ont he other jar, but then stopped, but then it had been sitting open.