OK I'm confused is this right?? can a neigbour one house down start requiring for us to pay his bill because we are the house at the beginning of the road. Who's to say the house at the bottom of the road start asking for money for his blocked drains?? Seems to me a bit cheeky?
Yeah, I remember you guys had trouble with this before, didn't you? Unless there's something written into your lease or mortgage that the bills for plumbing are to be split between all parties, I don't see how you're required to pay.
I think, in your position, I might do the following: ask the guy to get a detailed bill for the work done. If you feel the plumbing has considerably improved due to the work done, you might offer to pay some of the bill if the work done vs the bill doesn't seem too outrageous to you. If it does, offer to get involved with all parties the next time work needs to be done so that everyone knows what is going on and everyone can make a decison as to whom to use for the work and how much everyone is willing to put into the kitty. It's just a way to keep a bit of peace, really.
There's no reason anyone but the person who called out the plumber should pay the bill, just thinking that if paying a piece of the bill keeps the atmosphere around your home peaceful,it might be worth it.