The main reason not to wash your rag quilts at home, is all of the strings can plug up your machine, and if you are not viligant about emptying your lint trap in the dryer, you could over heat it/cause a fire.
The threads will break down, but it takes considerably longer than toilet paper. As to causing a problem to your septic tank? That depends on how well the rest of the sludge is breaking down, and how many of these quilts you are making.
The $3-4 dollars it costs to wash these in a laundra mat is nothing compared to what you could spend later on washing them at home :wink: :D:D:D