Then, continue to flip it, but invest your profit (only) in your rentals.Buying rentals is "spending" your money. 

You can also start playing around with the calculators and doing mock analyses on potential deals to start getting a feel for the market.

You have to think what would the borrower do, continue paying a house that is $20k+ upside down at higher than rent values or stop paying, let you foreclose, live free for a year+ during the redemption then go rent a place for $600. 

Playing the small ball shell game :)

Also, state law plays a major role.

Mahalo, much continued success. 

Anyway, glad you found a way to pay it off that made sense but I love sharing the asset depletion approach since I know so many great real estate investors also play the tax strategy well enough to end up with DTI issues.  

Be persistent, and continue to learn. 

Instead I would suggest you continue to learn as much as possible.

I am obviously going to continue looking but I appreciate your experience on the topic.