First thing is always change the drain to a full bore ball valve. Yours is probably clogged already. So buy this and this first.
https://www.amazon.com/Aluminum-Eau-...s%2C999&sr=8-3
https://www.amazon.com/House-Mods-HM...s%2C517&sr=8-5
But for now we need to clean out what you have. Attach your garden hose to it and take the end out side. Get an air compressor with a blow nozzle and a bucket. Open up the valve on the heater and blow air in it by way of the hose putting the hose in your bucket to see your crap. Repeat till clean. Replace as instructed. Repeat yearly or as needed.
Short bursts of air don't blow up your tank. Play with it till you find the best blast.
Your electrodes are most likely fine they are just buried in slag. Might take the bottom one out and rig up a hose to vacuum out the crap.
If yours will not drain shut your water off. Then relieve the pressure then keep all closed to make a vacuum and quick change your valve.
You will need an impact to remove the rod. Just tap it lose then hand remove and install or you can do damage slinging it around.
