Shower drain gunk
I bought a 2011 25' a few months ago which was in great condition. I noticed the shower drain was slow, but until today, it was not a problem. After returning from a trip I noticed some brown grit in the bottom of the shower stall, and the drain was completely clogged. When I used a plunger to try to free it, it pulled at
1/2 a cup of brown grit that looked like coffee grounds into the bottom of the shower. I'm not sure if it is rust, but it has the hardness of rock, almost like lava rock with partical size like sand.
Again, I'm concerned because of the large quantity of this stuff that I pulled up. I'm not familiar with the plumbing yet, but I assume the shower drains directly into the grey water tank. If so, what could this be, and do I have reasons to be worried?
Thanks for your help.