Regarding emptying the waste ink tank, I can put more details down.
I have heard a rumour that non-Canon ink manufacturers are considering legal action because Canon are stating their inks to be the cause of faulty print heads, when in fact wear and tear is the source of the problem.
Ink formulations are very similar, and those inks are rigorously checked, so I would be wary about such claims.
For anyone with a BJC600 series printer, I recommend you halve the life expectancy of the print head that they suggest. From my own experience, and from what ex-Canon engineers have told me, their recommendation is very optimistic.
Does anyone have more information on this?