Sure , you can use the equity in your ppor. It gets it working for you . The only trouble is the interest for your ppor is not tax deductible while the interest for the rental is .
Interesting that you say the mortgage is too big to pay off ? So you are working on the capital gain in the rental to increase enough to settle your debt ?
Have you calculated what your average capital gain and time period is ( less cgt ) to achieve this and compared it to paying down your mortgage ?
Nothing wrong with using leverage in this way but I'm just wondering how the numbers stack up ?