We have been using TankTechsRX for a number of years now and have had no issues with our black tank, but we never leave the drain valve open, and we drain the tank once a week. Granted, the sensors don't work, which I never look at anyway. On the TankTechsRX web site, they talk about how to clean a black tank, and how to contact a professional that can deal with the pyramid.
http://tanktechsrx.com/unclogging-yo...ank-or-toilet/