A brownish or dark red stringy substance sounds more like the RBTA is expelling its zooxanthellae rather than just normal waste product. When they expel their waste, its usually white or clear and kinda looks like slime. Usually its not a good sign if its expelling its zooxanthellae and will eventually look bleached out if it continues. However, sometimes they will get rid of some if it's lighting has changed, especially if its trying to adjust to brighter lights or a longer light schedule.
Just keep an eye out for bleaching and if it keeps spitting out its Zoo. you might want to check all of your tank parameters. Also look for signs that it's trying to hide from light.
If you haven't already done so, look over this great pdf. on anemone FAQ (found here on reefcentral).
http://www.carlosreef.com/AnemoneFAQ.pdf
Good luck friend!