There is a 250 marine tank in my wifes office. The office owns the tank, and inhabitants. They pay someone 800 usd a month to maintain the tank. after talking to the guy that works on it, i find out that he owns a several tanks out in town. a few at rubios and some hotels downtown. the buisnesses lease these tanks from him from around 300-1700 usd a month, depending on size type. thats a decent living right there. and doing something that you love helps a lot.