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To replenish the solution with some acid every now and then and allow air-contact. There is no need to get rid of the copper, in fact, the copper in solution helps etching the PCB. Finally, you hardly won't need any additional FeCl3. The only thing used up is acid.
Initially the iron(III) acts as oxidiser, but later on, the copper (II) in solution also acts as oxidiser. The resulting copper (I) compounds are VERY easily oxidised by oxygen from the air. So, essentially, oxygen from the air is your free oxidiser. The only non-free compound (after the initial FeCl3) is the acid HCl.
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