Bring an air compressor with fittings, hook it up, go around listening for air leaks.

However, be cautious as banks may still enforce the clause if they detect the transfer of control.

The hard part will be finding the leak in that case.

Quote from @James Nix: It's obviously a leak and the most likely culprit is the toilet.

Have a 1960s 30 unit single story motel where we are coming up on some end of life issues: the cast iron plumbing is disintegrating underneath bathrooms, radiators are starting to leak, electrical is in poor condition, and just today, discovered significant termite damage affecting multiple rooms.

What about the plumber that stops a flooding leak on a Sunday morning or the HVAC tech that fixes a furnace under a crawl space in the middle of a freezing night?

Any company insuring your properties without an inspection most likely has a clause buried deep in their policy allowing them to deny claims for conditions found on the property that do not meet their UW standards and they will deny you claim based on "the house should have not been insured with them anyway".Although the inspections can be annoying look at it from the other side.You pay them 1000 to 3000 a year to insure a rental property where they agree to pay out possibly hundreds of thousands of dollars if it burns down or up to 1 million if a tenant slips on a bananna peel and falls down the steps or the tenants dog bites someone and since you didn't enforce the tenant having their own renters policy to cover the dog bite the landlord's policy is paying out.The insurance company is very much like your rich uncle backing your business venture - you run the business, he takes on the financial risk from disasters, and doesn't even get a say in who lives in the property.Your rich uncle asking you to fix the steps, put up a handrail, etc which is in your and his best interest long term.Do you really want to rent out a property with a busted front step and a bad roof that is going to leak sooner than later?

Update: I just had one of my mini splits leak into an interior wall creating some damage to my awesome 1912 Craftsman.

The downstairs neighbor came up to tell my tenant that he has a leak in his bathroom ceiling, which is right underneath my condo's shower.

I have a unit that has a small leak in the flashing outside the ceiling.