The thing you have to be SURE of, when draining the hot water tank is to ALWAYS turn off the electric heating element switch (if applicable to your model of water heater). Not all water heaters are propane and electric.....but some are both.
Failure to do this, will burn up the electric heating element.
If you have a Suburban brand water heater, you drain it by removing the anode rod on the front of the heater.
This may help too:
http://www.forestriverforums.com/for...ore-36197.html
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If you have the Atwood brand, it usually has a plastic drain plug on the front:
It's usually a good idea to only drain when the water is cool, as having hot water hit you (as happens a lot when you try to drain it), will ruin your day.