It seems that he has bought the land that has the benefit of the covenant to use the pipes.
However, the covenant fell into misuse years ago and was surrendered/ abandoned by the previous owners of that land who not only stopped to use it but installed a separate system.
The covenant or easement fell into misused at that point and cannot be simply resurrected because it suits the builder.
In addition I very much doubt that the pipe is fit for the purpose he wishes to use it for. I would contact your local council and have a chat to the building regulations department just to get their view.
Hi if it is in the deeds at all it suggests this is not just a casual arrangement or licence between that vendor and that purchaser as such personal agreements do not end up being mentioned in the title deeds.It could be an easement or covenant it pretty much adds up the same
The land that the builder has bought has the benefit of this right and it may be that the builder is simply trying to push what they see as their right. However the position with property changes and rights can lapse because they are no longer used or appropriate . If a different system was put in place and no owner of his property has used it then it has fallen into disuse.
In any event it was not designed to be used for 30 houses sewage and water it related to one property.
Your point is not to dent it existed but simply recite the history. As I suggested speak to your local council you can enlist some powerful allies that way.