Lets see if I can describe this...

[G1GY]

Originally Posted by Fish

Gary,
Is it because the water wouldn't drain through the sand fast enough?
Thanks,
- Chad

Yes.

Fine sand will make a more positive seal because all of the granuels will just fit together sort of like lego.

I'm just wondering.

What's to stop the whole tank from draining down if you have a cracked, broken fitting or hose?

If it's a check valve, those things are not very reliable IMO.

Maybe a small standpipe hidden inside a rock pile for safety would be a good idea?

That way you could use fine sand and have a little peice of mind that you'd never loose all the water in the tank.

Just a suggestion though.