Communal storm water drain blocked by solidified grease

I live in one of six detached houses on a communal drainage scheme in DunLaoghaire Rathdown. Some years ago my neighbour Mr X, who is the first house at the highest point in the drainage scheme, had his drains unblocked by some cowboys. The next day serious amounts of solidified grease and pebbles came out of my storm water drains onto my patio. My drains and AJ were full to the brim with dirty water. Mr X refused to take any responsibility and shut the door in my face.

I got a drainage company out who said that it looked as if Mr X was putting foul water into the storm water drainage system. They unblocked my drains but said it was a communal problem and suggested I get the Council out. DunLaoghaire Rathdown Council came out and wanted to do a dye test to find out what was going on. They wanted to put dye down our downstairs WCs. Mr X refused to participate. He has had an extension built which includes a WC and utility room. At the time I did not pursue the issue further.

However, today I found more lumps of solidified grease (and even a piece of pot scrub!) in my storm water drains. The drains and the AJ are full to the brim with stinking black water with white solid grease floating around. The two neighbours further down the drainage scheme have the same issue. We all believe this is an environmental health issue which needs to be solved.

I know from experience talking to Mr X is a waste of time. He does not have a problem and will not care that we do.

Does anyone know if we have any rights or what we could do? Does the Council have any power if we can show that foul water is being put into a storm water system?