They will be able to approve plans for an ADU regardless of the coastal commissions objection or they would know what the status would be of any CC stoppages. 

Our leases say that tenants are responsible for changing light bulbs and landlord is not responsible for damage from wastewater stoppages caused by foreign or improper objects in lines. 

For example, my lease states “Tenant shall be charged for repair of drain blockages or stoppages, unless caused by defective plumbing parts or tree roots invading sewer lines.”So, having not read your lease, we couldn’t say for certain who is responsible for the cost.

It’s possible the plumber push the stoppage down further with his snake.

I state in my lease that all drains are operating properly at the signing of the lease, and tenant is responsible for all stoppages.

This family has four children whereas the previous tenant had none, so it's pretty clear who caused the issue.My lease is clear:Owner will not pay to repair conditions caused by the Tenant, his guest or invitee or damage due to windows or doors left open, sewer/septic stoppages caused by foreign or improper objects in lines, or cosmetic items that do not impact the functionality or use of the item.

For example, my lease states "Tenant shall be charged for repair of drain blockages or stoppages, unless caused by defective plumbing parts or tree roots invading sewer lines."

Our rental agreement has a section about drains, cleaning and maintenance, which includes this line: "Tenant agrees to pay for clearing the drains of any and all stoppages except those, which a plumber who is called to clear the stoppage will attest to in writing, were caused by defective plumbing, tree roots, or a result of weather."

Owner shall not pay to repair conditions caused by the Tenant, his guests or invitees or damage due to windows or doors left open, sewer/septic stoppages caused by foreign or improper objects in lines, or cosmetic items that do not impact the functionality or use of the item.

@Brock Bonnicksen It isn’t uncommon to put in a lease a clause that covers sewer drains that requires tenants to pay the cost for stoppages except for those that are caused by defective plumbing, tree roots, or acts of nature