This should be covered in the title documents. Unfortunately, it is not as easy as just relocating he soakaway. Have you checked the deeds of the neighbouring properties to check whether there is rights reserved in their documents? If not, I would suggest that you do this.
You would need to obtain the neighbours' consent if they have rights reserved.
I hope this answers your question. If so, kindly rate the answer and provide feedback.
If you have any further questions, please do not hesitate to ask.
If you have any further questions, please post them in this thread and I would be happy to answer them.