I was moving out of an apartment where I had a waterbed. To drain a waterbed, you are supposed to connect a hose to the drain valve and then connect that to the faucet and turn the faucet on; apparently water flowing from the faucet through the valve into the sink also sucks water from the waterbed. I left for an errand and came back to ALMOST an indoor pool; the bed was about six feet high and could have burst at any moment. Looked like an enormous tick. I went to the faucet and switched the faucet from FILL to DRAIN. Long story short, I was able to get my deposit back and sleep in the bed again :-)