Is the black water from new carbon filters dangerous?
No — it's carbon fines, loose dust from manufacturing. Unpleasant to look at, harmless to drink, and it flushes out in minutes. Still, flush it out rather than drinking it.
Skip this and your first glass looks like ink. Here's the 20-minute fix.
Two things need to leave your system before you drink from it: carbon fines (loose black dust from new carbon blocks — harmless but disgusting) and membrane preservative (the food-grade solution membranes ship in to stay sterile). Neither is dangerous; both make terrible first impressions.
Same logic, smaller: when you swap just the carbon stages, flush them 5 minutes before the water reaches the membrane — easiest is to briefly disconnect the tube feeding the membrane housing and flush to a bucket. When you swap just the membrane, flush 15–20 minutes.
No — it's carbon fines, loose dust from manufacturing. Unpleasant to look at, harmless to drink, and it flushes out in minutes. Still, flush it out rather than drinking it.
After the full flush sequence above — typically 20–30 minutes of run time. When it looks clear, tastes neutral, and TDS reads right, it's ready.
Yes, briefly — 5 minutes for carbon stages. A single-filter swap doesn't need the full 30-minute ceremony, but don't skip it entirely.
Yes, that's what the drain line is for. Or into a bucket for plants — flushed carbon water is fine for watering.
Unlikely. Some carbon blocks are dustier than others. Keep flushing; if it's still gray after 30 minutes, check that the filter is seated correctly and not bypassing.