Hi all. I dumped my black tank and it was very slow in draining. After I dumped many buckets of water into the toilet, it worked better. After flushing the sewer pipe, all this gunk came out. Kind of looks like rusted pieces and very brittle. Calcium deposits? The black tanks are plastic correct? We go camping about every 6 weeks here in Florida. After dumping, I always put in about 3-4 gallons of non-potable water and about 4-6 ounces of the orange TST Max toilet treatment...