what keeps a wet/dry filter from draining your tank?

Question

say power goes out what keeps my water from just draining out of my sump in my wet/dry filter onto my floor

Answer 1

Most are gravity fed, if the outtake from the tank is from the top of the tank obviously when the water drops below the outtake that's it no more water leaves.
If the out take is from the lower part of the tank the control needs to be in the sump, where by a float blocks the intake into the sump once a certain level is reached.
Your worse nightmare comes if the outtake gets blocked and your pump continues returning water from your sump now that's messy.....

Answer 2

If your tank is not drilled you have a skimmer that pumps the water into the wet/dry filter if this goes of the water does not go into the filter.

Answer 3

check into an over-flow box,these can help allot.they hang on the back of your tank.this will help if your tank is not reef ready meaning you don't have ports drilled for your tank.Also try doing away with wet dry system and move on to a good canister .I did all that wet carpet and dead coral is scary.Good luck