FWJ,
you mentioned that this guy is a friend of a friend and he referred you to him to begin with? are you the least bit curious as to if your 'friend' knew how this guy was to begin with, or at the least, that he was having major problems with his septic tank before you came along? if so, then this 'friend' of yours doesn't sound like much of a friend to me. just out of curiosity, who's side is he on, yours or the other guy? are you counter suing for non payment? hope this works out for you, that's a shame to hear that.