Most drain plugs you see for bathtubs are worth a sh. for stopping the water effectively. You gotta get one of those marine type rubber plugs, in the appropriate size, with the nut from like westmarine.
That bag sounds like a very good idea for potable water storage. But even tho it's in a bag, does it need any kind of treatment? The natural occuring microbes in tap water would love to have a party in a nice sealed warm plastic bag. Just a thought.
New to the site and glad to see there is a survivalist section. My family and I are also concerned about natural disaster and numerous other unforseen possibilities. Glad to find some like minded people instead of the "Morning of" individuals that are raiding all the shelves and gas stations when the SHTF or the Zombies come...
Cheaper than Dirt had these for $20.00 recently. I have never personally used these. I am from South Texas and have weathered quite a few hurricanes when I was growing up there. We always filled the tubs and almost always lost power, shortly followed by the water. If your going to fill up your tub, Do yourself a favor and clean it real good first. Even treated water doesn't do well with soap scum and other stuff that is living in a bathtub. I recommend pure bleach as it kills most anything.
As far as treating water, you can use pure unscented bleach treat water. Do not use NON-CHLORINE bleach. 1/8 teaspoon for gallon of water, stir it, cover it (hard to do in a bathtub, but with duct-tape anything is possible). You should be able to smell a chlorine smell after about 30 minutes, if not, repeat same. If the chlorine taste is too strong, let it sit uncovered for a few hours and some chlorine will dissipate. Syphon as necessary, but keep it covered (this keeps the chlorine from getting out). It isn't DASANI, but its potable and will keep you from de-hydrating and being on the obituary pages when the papers start printing again.
If the water goes out, you can drain your hot water heater as necessary into a sterile containers. Be careful doing this, it would suck to get seriously burned in the middle of an emergency.
If your bugging out, there are numerous portable filters and pills available. I have drank river/lake water on numerous occasions using water treatment pills and have never gotten ill. FILTERS DO NOT TRAP/KILL LEPTOSPOROSIS! (http://www.leptospirosis.org/topic.php?t=15)
Follow the directions explicitly and don't for get to treat the cap/thread on your container when you are using the pills. It only takes one of some water-borne critters to get you very sick. Don't let an emergency be the first time you try treating your water. Practice, then practice again..