Just as I now always look at my friends' garage doors to see what they need help fixing, now I'm constantly looking for brown stains in my friends' toilets. :)
Here's one I found at one friend's house:
And, here's another, at a different house:
There were many new lessons learned though, mostly from being way too casual around the acid and therefore making a few mistakes by not being cautious enough.
For example, my hands are killing me, because I cupped the acid back and forth to cover the stains in an attempt to speed up the process:
Another lesson learned is to remove the baggie over the filler tube when you start refilling the toilet! I left the baggie on to get the phone, and when I came back, acid was all over the stone floor (making it slippery to the touch!).
Another lesson learned is that you can peel back the plastic wrap over the bowl to scrub the stains to move the process along quicker - but - you'll get one hell of a few good coughing fits out of being that close to the open bowl of acid. My chest is still hurting - like when you have bronchitis:
Yet another lesson learned is that some people are really picky when it comes to chemicals. This shot is at a friend's house, where I didn't bother with the funnel and just poured the acid directly down the tube. Of course, a lot went into the bowl - which smoked and fumed. Hours later, my friend swore she could still smell the acid (although I don't believe her):
Another lesson learned was that the plastic wrap actually works BETTER than does the rubber banded sandwich bag, especially when you remove it to pour more acid. The plastic wrap throws away more easily without keeping acid in all the folds:
Another good lesson was to not get cavalier about the acid. Here you see me pouring it directly on the scrub brush in the bowl. Problem was that droplets of acid started burning my bare skin within minutes - even though they didn't hurt at first.
In summary, the biggest thing I learned is that the damage from the acid doesn't hurt too badly at first - but it lingers on.
Also, I learned you can clean the bowl directly, but, you'll get a few whiffs in your lung - which you'll know when you get 'em as you'll start coughing away immediately.
The splashes on the bare skin only tingle and burn at first, but later little blisters will develop on your fingers. No big deal - but it would have been better had I taken the stuff more seriously.
Anyway, hope others benefit from the experience outlined here in pictures. If you have questions, ask away.