I have a customer that wants a drain installed, and of course wanting to make my customer happy, I accepted the challenge. I don't know what to charge for it though. How do you all charge for installing drains? What are key things I should keep in mind and look out for? I've installed drains before, I'm speaking of common mistakes made financially... i've already underbidded two projects i'm stuck in now, i'm afraid if I do another it could be the end of me and mine... any advice?