Hello - simple question please. I just purchased a Grundfos circ for a wood-fired radiant system that I am building, and there are no instructions as far as how to connect the flanges. Seems simple right? But I obsess over little things. So the O-ring is in between the flanges, but I feel like if I tighten it so that the flanges contact each other - the O-ring will split. So how tight is too tight? Do I go all the way?