What is the ruling of Islamic law on using water from a household tank that overflows into the street, causing harm to neighbors, and preventing its owner from relieving himself and performing ablution in his home?

The Sharia has magnified the right of the neighbor and prohibited harming him, to the extent that whoever's neighbor is not safe from his evils will not believe and will not enter Paradise. Harming a neighbor is among the major sins. Gabriel (peace be upon him) advised the Prophet (peace and blessings be upon him) so much about the neighbor that he thought he would make him an heir.

Leaving a septic tank to fill and overflow into the street is a great harm to neighbors and the general Muslim public. It causes pollution, diseases, and defiles clothes and shoes. It is akin to defecating in the road, which is a cause for curses. Therefore, the tank must be cleaned immediately when it is close to full, and it is forbidden to leave it to overflow into the street or the neighbors' homes. The people of the village must address this problem by installing a sewage system.