I can not imagine why glue at the toilet pipe would effect the draining of the black tank. Even air does not pass through there while dumping, unless you open the toilet valve. Did you have a lot of "paper" hangups while flushing. My guess the slow draining was caused by improper venting (where no air gets to the tank creating a vacumn) or like others said the disc caused by drilling holes into the tank (2-3" holes and one or more were left in the tank. Don't forget, only the highest quality labor is used in making an RV. YEA RIGHT