Could there be a sinkhole under my house?
	
	
		About 4 years ago, my bathtub had a really bad clog. Whenever I used the washing machine, it backed up into the bathtub but never drained. I called 3 plumbers, and not any of them could unclog it. Then suddenly one day it was unclogged. But for about a week whenever I used the washing machine, it still backed up into the tub, but for that week, each time it backed up, about half a pound of small pebble like rock came up with it. There's no way that could have been a clog, so I have to believe that a pipe had probably burst. But since the tub was draining good, and after that first week, I was able to use the washing machine without it backing up into the tub anymore, I never did anything about it. Now with all these sinkholes happening, it got me thinking... All of that water in the tub each time I took a shower had to have been draining somewhere, correct? 4 years has past. Could I sort of believe that I have a good sized sinkhole under my house?