Homemade float box part 2

[markr]

So it looks like I will go ahead and make a homemade float box as a couple of people said they work but I do have a couple more questions about it, 1 how big of a float box pan do I need? I'm going to use a 1 inch outlet and 2 where do I need to mount it? I'm running 7 inch flues, so do I mount it at say 6.5 inches on my pan?