The limit of coverage reflects the estimated cost to rebuild your home if it is destroyed by a covered event.)Home Protector (This endorsement will provide additional coverage if the amount of a covered loss exceeds your Dwelling coverage limit because of increased building costs, building code changes, inflationary effects from material shortages or additional debris removal expenses.)Personal BelongingsOther StructuresLoss of Rental IncomePersonal Liability Medical Payments to Others Should I add-on these coverages:Water Backup or Sump Pump Overflow (This provides coverage for non-flood-related water back-ups through sewer lines and drains, and overflow from sump pumps (machines used to remove water from the foundation or basement of a home).)Slab or Foundation (This provides up to $15,000 for damage to the slab or foundation of your home if the damage is caused by accidental discharge or leakage of water or steam (including constant or repeated seepage) from within a plumbing system or household appliance.

Whoever does the soil sample and pulls the tank is on the hook for leakage.

Measure the size if it and leave it hanging so there can be no water leakage through the tied off part.

Typically you will be able to see if there has been any leakage.

Mildew, mold, water leakage, lead paint, rotting carpets, etc., IS a health issue.

However, my partner is worried about water leakage issues and whether such units could handle tenant abuse.

Did not have any rent records as well. there was also a leakage problem we addressed with the seller and on 26th got a confirmation that they are willing to address it. 

There's a risk of past leakage or leakage during removal.Here's a scary story -http://community.seattletimes.nwsource.com/archive/?

A vacant policy typically excludes the following, Vandalism Building glass breakage Water damage Theft or attempted theft Sprinkler leakage (unless the insured has protected the building against freezing)A builders risk policy will typically cover these perils.An added coverage the Builders risk covers is  "Property in Transit". 

I have come to a point where I just accept some leakage for these types of situations, sad but true.