looking for info on water tank comparisons I came across this site
Emergency Preparedness: How to make sure your water heater can be used as an emergency water supply
There they discuss a lot of issues with various hotwater heaters including ultra slow drain times, crap in the tanks and the crappy drain valves clogging and leaking. They recommend replacing the drain valve with a better off the shelf one to allow you to actually get all of the water out easily/quickly in the event of an emergency and you needing to drink that water.
They had tons of info on the tanks, various setups and options.