That's really odd since the DOS is supposed to be a peristaltic pump... at least that's what I thought.
I guess not!
That sucks.
I always had my dosing containers above my GHL doser and no problems.
They are peristaltic. The problem is that p-pumps can still siphon. My only hesitation in the DOS is the 2 roller setup. If they release a 3 roller head, I will buy upgraded heads.