For the pineapple orange syrup, dice the pineapple and oranges. Mix with the sugar and lemon juice and bring to a boil.
Boil for approx. 7 minutes until bubbling. Then strain the juice (use a sieve to remove the coarse pieces and a coffee filter to remove the fine ones, if desired) and bring to a boil again.
Bottle the pineapple-orange syrup.