This gives you a good view of not only the septic lines but also the tank.

Instead of only buying single-family homes, for example, you could invest in multifamily homes, self-storage facilities, and mobile homes.

On that note, I highly recommend do not ever skip the permit process and always check in with the city;  Not doing so can quickly tank any deal.

to buy land and develop RV Park for long-term guests and/or self storage...

- for an underground oil tank that was already removed but that was just never closed with the contractor or seller?

Are you looking for a specific niche, such as self storage or multifamily?

In my case, I have residential rentals in one LLC, commercial properties in another, self storage in a third, and my real estate company operates in a fourth.

Quote from @Sarah Kensinger: It's not a waste of water if you're on a well and the hot tub is drained in the yard, which the ground would soak up.I was going to say this^^^^^....most people don't realize that all water that goes into your septic tank, or in the ground, goes (eventually) back into the ground and filters (generally) down into the aquafier.

In my case, I have residential rentals in one LLC, commercial properties in another, self storage in a third, and my real estate company operates in a fourth.

If they continue smoking, you'll have to put up with it until their lease is over.In the future, make it clear that smoking of any substance is forbidden inside any structure, including garages, storage sheds, etc.