I live in a terraced house. My drainpie leaks on the joint between the two propertys. I have flash taped up the joint that was on my side but water is still coming out. I think the down pie may be blocked. The down pipe is on the joint between mine and my neighbours propertys and services both. My neighbour is constantly leaving notes and calling round to ask me to fix it. Is it my responsibility to sort the joint downpipe?