Rheem model 81SV-400a

you connected to the drain valve, open valve ccw. See page 21.
https://manuals.harborfreight.com/manuals/64000-64999/64686.pdf

Dear Chu,
I think I am hearing you say the water is hotter if the water heater has sat all night without the usage of any hot water, and otherwise, it is not hot.
I should suspect one of your heating elements is not good any more.
Look and see if there are 2 removable covers on the side of the water heater, an upper and a lower.
Take a test instrument and, with the water heater unhooked from the power source, see if you have one element that shows no continuity with an ohm meter /resistance test.
That element can be replaced, sometimes you must drain the water heater water to do so.
God bless your efforts.

its for drainage to extend the life of the tank you should drain 2-3 gallons of water every 6 months ... this helps to remove residue from the bottom of the tank

If the drip is coming out of drain valve: Put a hose cap over end of drain valve.
If water is seeping out of cracked drain vale, then replace it.
If the leak is seeping around previously sealed threads, then tank may be rusted beyond repair.
http://waterheatertimer.org/How-to-replace-water-heater-drain-valve.html
http://waterheatertimer.org/Leaking-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Look on label on side of tank.
Wattage of tank will be element wattage. This is true if tank has one or two elements since both elements are never ON at same time.
Simply go to hardware store and buy 3500W element.
Take phone photo to store if needed for identification.
http://waterheatertimer.org/How-to-replace-water-heater-element.html
Wattage appears on end of each element.
http://waterheatertimer.org/How-to-test-water-heater-element.html
http://waterheatertimer.org/images/Voltage-printed-on-element-.jpg

The plastic drain valve is a possibility. Also the Temperature/pressure relief valve is typically piped close to the floor if there is a drain near by. People tend to ignore water heaters. The TPR valve really should be excersized annually. If it won't re-seat, then it should be replaced. Second the tank should be partially drained annually to drain any solids that have accumulated in the bottom over time. If you don't do this frequently the drain valve can become almost impossible to operate.

The tank may be corroded and you may need a new unit. Check to make sure that the water is not coming from any of the water connections that are higher up on the unit. Also check the drain plug to make sure it's secure. I don't know the age of the water heater but it may be time to replace. Most people don't know that water heaters require maintenace (draining the tank to remove sediment) from time to time.

If you are reffering to the drain valve at the bottom of the hot water tank. It may be leaking due to the O ring being cracked or worn out. You can either drain the tank and replace the valve or you can buy a hosebib brass cap and thread it on the existing valve. There is no cause for alarm when doing this as this valve is just to drain the tank when replacing your hot water heater

You can repale it, but yes the tank will drain


Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

1. turn off the electrical power first.
2. attach a garden hose to the hose bib attachement on the bottom of the water tank and run the hose outside to allow the water to drain out by gravity.
3. Turn the valve that is on the inlet of the water heater. Now that the power is off, you can drain the tank.
4. open the drain valve where the hose has been attached.
5. To release the pressure, you can open a hot water faucet in your kitchen. This will allow the water to drain out easier.