If you have high rust/sediment content in your water, you should flush your water heater at least annually. If you open the drain on the tank and only get a trickle, your tank may already be partly filled with sediment.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.