Neighbour is not allowing re construction of sanitary chamber

Have you obtaied the necessary building permit from the municipality/panchayat?

First take permission from municipal authority of your area for reconstruction of your sanitary chamber. 

Yes, neighbors can object to the reconstruction of a sanitary chamber if it impacts them or violates any local regulations. They can do so by filing a formal objection with the relevant authorities or through legal channels if the construction is causing a nuisance. However, if you have obtained the necessary permits and the construction is within legal bounds, your neighbor's objections may not be valid.

It's 30 years old building , what permission I need to take for existing chamber , i need to reconstruction the older one 

Attached is the Pic of chamber 

You can approach the local municipality and submit an application as is required to be submitted as per procedure giving all the details and attach the necessary documents, to sanction the permission to construct the sanitary chamber.