After these tenants move out, I'm thinking of just keeping the rental empty with furniture. It sounds stupid to give up $4,200 a month, but I really hate dealing with the homeowner association, move-in/move-out rules, and maintenance issues. Given that the condo doesn't have a mortgage and I have to pay taxes on some of the rental income, I'm not giving up that much. The condo can be a place for my sister, parents, or in-laws to crash when they want to stay in SF for longer than a week or two.
Generating passive income requires upfront work. Some say achieving passive income is actually quite an active pursuit. Some paths may be. But then they may not be truly passive income investments. Acquiring a passive income producing investment can be very simple, even if there are many others behind the scenes doing a lot of work to vet, package, and manage that investment.
As a private lender, you can lend to anyone in your social circle. For example, many home rehabbers need access to a source of capital they can tap into very quickly in order to fund the initial purchase of their properties. You can partner with a rehabber who uses your capital for a short-term in exchange for an interest rate that is mutually agreed upon.
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property.  Check out RealtyMogul to learn more.