common drains
Hi.
Im not a legal expert but I am in the same situation as yourself. My drain is shared with the house next door. This is very common apparently with dublin artisan houses where the main drain can be shared across 2 or more houses. The house next door belongs to an elderly man who's frequently in hospital and similiar to yourself I found out about my drain when it blocked and we needed to enter next door to clear it.
(Until this point I didnt know that I shared this drain, my surveyor didnt inform me of this and it was quite a shock).
Anyway, I dont know if this is any help to you, but I approached the son of the man next door and together we set up a legal agreement on the ownership and responsibility of the drain, protecting both of us if either choses to move. We have shared the cost of unblocking.
hope that is some help.
good luck
c.