Our water heater is on the second floor and we need to have it flushed. It has a drip pan with a hole that has a tube attached to it. Common sense tells me that I can flush the water heater directly onto the drip pan since it has a pipe attached to it where the water will drain, but I haven't seen anywhere on line that this is okay to do. I've read only that it is there just in case there's a leak. Can I drain our water heater onto the pan or should I attach a hose to the it to drain?
The drip pan's drain tube may not be large enough to handle the flow if you drain the entire water heater through it, leading to an overflow of the drip pan. I would be safe and use a hose to connect the outlet to the drain.
I'd suggest you use a watering can or pitcher to test where the drain tube goes before you crack the hot water heater drain. Pour a half-gallon to a couple of gallons down the tube and see if it shows up somewhere below. It probably should be more or less directly below in the basement, but it's always a good thing to check that it works before asking it to do too much. If the wall or ceiling on the floor below suddenly starts weeping water, at least it will be a small amount, and you'll know you should get this fixed before you have a leak, and not use it now.
My recollection is that this sort of thing is not likely to go into the sanitary sewer - dumping on the basement floor, or possibly into a sump, is more likely. You may want to move things in the basement before dumping 50 gallons down there, if that's true. It should be less than 12" from the basement floor.
The drain on the safety pan is for leaking heaters only, not for draining.
Shut off the heater via the breaker or shutoff. Use a heat resistant hose (make sure hose washer is in good condition) and place the other end in the bathtub or equivalent. Then, slowly open the drain. When you're confident the hose is sealed tight, there are no leaks, and half the heater has drained, then and only then slowly open the safety drain on the side. That will hasten the draining.
Be careful: water may scald you and cause injury. Also, shut off power to the heater before draining. It is best to let the water in the heater cool off first.
I have tried flushing our water heater with the drip pan and it overflow. Good thing that we are located in the basement. But that still sucks :( Better use a hose for the draining.
I say go for it: as a bonus you get to test the operation of the drip pan (where exactly does it go? Is it indeed large enough to handle a flood event?). Just start slow, have towels handy, and be ready to shut it off... quick.
Don't forget the water is... um...hot.