Hi,
Shut the water off.
If you are replacing the unit open the PT on the water heater.
Hook a garden house to the heater drain.
Use a washing machine hose ( 2 Female ends) hook to end of garden hose.
Open the heater drain if no water flows hook the other end of the washing machine hose to a hose bib. Turn the bib on and run the water backwards into the heater to loosing up the sediment.
Good Luck Woodbutcher

Thanks for the alternate idea Woodbutcher! But I'm not sure what "PT" means....pressure valve?
I can see where reversing the water flow would pop thru the sediment but reclogging might occur almost immediately as this crud has had years to accumulate and thicken up. This sediment has to be a few inches deep inside there. Let me know what PT means, a little challenged on plumbing acronyms :) thanks

After 38 years on well water the sediment is more like a cinder block than a pile of sand and gravel. Reversing the water flow is likely to do nothing.

More than likely you'll need to remove the drain valve and drive a star drill or other implement into the sediment to get the water out and it will be messy.

The afore mentioned ideas are great, and I would certainly try them, but in a worst case scenario if they don't work remove the treaded fittings from either the hot or cold taps on top, which will leave the 3/4" female hole open, then get a cheap 1/2" vinyl garden hose and cut one of the fittings off the end and push that hose down in the tank until it hits bottom, then pull it up just a bit use the hose to sypon the water out to a floor drain or sump pit.

Once you have siphoned as much water out as you can, you will have substantially reduced the weight and you can now strap the water heater on an appliance dolly to move it.

The stiff wire method worked for me, but it was in an unfinished basement, so I wasn't worried about a mess. OTOH, it still drained fairly slowly so there would have been time to attach a hose.

Wow, thanks for the extra ideas! I may end up trying them all in sequence until one works (starting with the least messy and easiest :). But still I will need to cut both H/C copper lines before doing anything so if no one sees a flaw in my original draining proposal above it might be the first attempt. This job is still at least 2-3 weeks off so your input is still greatly valued and appreciated. Once it's done I'll let you all know how it went.

how does a tank that is filled with crud heat water well?

The crud in the bottom of the tank cooks into a solid mass like ceramic and the heat energy will go through that mass into the water the same as if you had a ceramic baking dish in your oven, however, that thick cake in the bottom also has a tremendious insulating effect so while the water heater can still heat water, the efficiency falls goes out the window as the heater has to work three or four times as long to heat the water, and if left long enough it will reach a point where the water heater can barely make warm water, instead of hot water.

It must also be understood that there is a spiral deflector in the vertical flue up through the heater, which helps keep the rising heat in firm contact side of that tube rising through the water vessel, so you still get a substantial amount of heat through the vessel wall, even though the bottom of the tank is obstructed with the sludge.

update ---
Haven't gotten to the point of draining the tank yet but thought I'd check back and give Lazypups idea the thumbs up for first choice. I ran into an old friend who's a Mr Fix-it jack of all trades and he too says to remove the hot water line from the heater and insert 1/2" pex line connected to the outflow siphin hose. After a bit more research it appears that the interior H/C lines do not go all the way to the bottom of the tank so lowering a piece of pex into the Hot line (the shorter of the two inside) would be best way to get the most water out.....still a couple of weeks off....

You will actually do better to put the siphon hose is the cold water side. The hot water fitting has no tube in the tank, it is just a 3/4" female iron pipe fitting welded on the tank wall, but the cold water line has a plastic "Dip Tube" which extends down almost to the bottom of the tank. The purpose of the dip tube is to insure that incoming cold water will go to the bottom which forces the hot water off the top of the tank. If it didn't have that dip tube cold water would enter the top and take the path of least resistance and go out the hot fitting, thus you would get no hot water even though the tank is full of hot water.

PEX tubing or vinyl water hoses are rolled, therefore the material has a natural curl. If you insert the line in the hot port that line can curl once inside the tank and the actual open end could end up fairly high in the tank making it difficult to siphon but if you insert it in the cold port it will go down the inside of the dip tube and remain near the bottom where you will be able to siphon nearly all the water out.

10-4 Lazypup! Will go in via the cold inlet.....I get the distinct feeling that you are not "lazy" :)

Drum rrrrroooooolll...:)

Well after 6 weeks of stalling I finally got er' done!
My first attempt to drain the tank did good, I used the "siphon water out thru the cold or hot lines" method. The only glitch was that the 1/2" insertion pipe was too large, it went in about 3" and stopped, it wasn't crud but a junction point, maybe. Used 3/8" and did ok, took over an hour to empty. The odd thing about it was that as it was emptying (thru translucent pex line) I used a flashlite shining thru the line and did not see much crud getting sucked up, guessing most is rock hard?

Thanks for the support to All of you! In a nutshell it was just 3/8" pex connected with an L to a 1/2" water hose (super glue and clap :) The end of the outflow was 5' lower than the WHeater. The best way to get the siphon started was to force water (via another hose) up the line until it comes out at the WH end, then shout to wife to unplug the water and immediately insert the 3/8" pex end into WH, I used the hot outlet, worked a-ok.
Thanks again for the help!

thank you for posting this. My heaters are in the attic, so removing the drain and fishing out the debries is not a viable option. I tried the hose backflow attempt too..

but the 3/8 pex, elbow to hose fitting and drill pump worked like a charm, less than 10 minutes to empty.
this tool is now hanging on the wall next to the water heaters.

One can mitigate buildup in water heater tanks by treating hard water at the house POE (also dramatically extends the service life of water heaters, plumbing, fixtures, and appliances) and routine (at least annually) draining water heaters. That's what that valve near the bottom of the WH is for.

My water was 26 gpg hard (last year went up to 45 gpg hardness) and WHers here last about 1.5 to 2 years. With a correctly sized softener and draining the WH every 6 months the WH I installed in 1996 is still working perfectly and when I drain it all I get is full flow from the drain valve of absolutely clear water. I'm ahead by not replacing eight 50 gallon LP water heaters at an average cost of $800 each installed for a total savings on WHers alone of $6400. Added plus is I have the only icemaker in the neighborhood that works and I haven't had to replace a washer or seal in a faucet nor had a single plumbing or appliance problem since 1996.

There's a tool on the market called a "Will Purge" that gets these tanks drained in about 20 minutes.

forget about all that stuff and just get a 1-inch diameter metal auger bit and drill a hole in the bottom and drain it through a funnel and hose. Done deal!!