I know that I'm guilty of not doing this regularly, my dad, a former pipeftter and practically a living parody of the responsible homeowner dad who drove us all crazy with preventative maintenance routines doesn't even do it regularly.
But it's really not hard, I'm not going to write a guide here because if you just punch "how to flush a water heater" into your search engine of choice you'll get plenty of good results.
It'll improve the lifespan and efficiency of your water heater and decrease how much sediment and such you have in your hot water.
Also when you get a new water heater, replace the shitty plastic valve they all seem to ship with these days with a proper brass valve, it's like a $10 part from home Depot and takes about a minute to swap them out. They probably use them because they know no one actually flushes their water heater anyway, but if you're one of the few of us who do, you know how sketchy the plastic ones are, if you touch them more than about 2 or 3 times you feel like you're going to break them.
How truly necessary it is will depend a lot on the quality of your water, if you have good, clean, soft water, it may not make a noticeable difference, if you have harder, dirtier water it might buy you a couple extra years with your water heater, and if your water quality is especially bad you may want to do it a couple of times a year. It takes a little bit for the tank to drain, fill back up and get to temperature, but it's less than 10 minutes of actual hands-on work, and you can go do whatever the hell you want in the meantime as long as it doesn't involve hot water.
You should also check and may need to replace the anode rod every few years, that can also increase the lifespan of your water heater. You're probably going to need a beefy impact wrench though, they often really don't like to come free.
I bought a house that was used as an office before getting remodeled and sold to to me. When I drained the hot water tank brown slime came out, it looked like a ribbon of brown mushroom. Gotta assume this was bacteria byproduct built up while the tank ran at low heat and saw little water use. I added bleach to sanitize while refilling it and drained.
This is probably something I should do ... the hot water tank predates my water softener. Truth be told though, I'll probably go tankless when it dies... my parents have one, it's such a nice small thing, particularly if your usage varies and your power is reliable.
Yeah, if it makes sense for your situation absolutely go tankless if you can, for a lot of situations they're going to be more efficient and save you money in the long run even though they're more expensiveup front
I believe it's still recommended that you flush a tankless unit once in a while, I don't have any firsthand experience with them though, so of course do your research , read the manuals, etc.
I don't know how you could flush a tankless, they're basically constantly flushing. It's pretty much just a pipe that runs around some kind of very hot heating element. There's nowhere to build up any sentiment. But still, quite a ways off any replacement.
As I understand it, and again I have no firsthand hands-on experience with them myself, this is just secondhand knowledge I've picked up doing my research over the years for when I eventually need to replace my current heater, ideally tankless heaters should be installed with isolation valves, you'd close off those valves, hook a pump up to them, and pump some vinegar through the heater for a while to dissolve any calcium and such that's built up. It's probably technically more of a cleaning/descaling cycle than what we traditionally think of as flushing, but it kind of serves the same intended purpose and some people are terrified of change so old terms tend to stick around.
There's no tank for sediment to collect in, but there is a bunch of tubing coiling around a heat exchanger and all those coils and bends are potential places for stuff to collect and build up in.
It certainly feels less necessary to me since like you said it's pretty much constantly flushing itself every time you run hot water, and things like your water quality, water pressure, and how often/long you tend to run your hot water for probably come into play somehow. I'd bet that like with flushing a traditional water heater a lot of, maybe most people can probably get away with not doing it and never have any major issues, but if you can remember to do it occasionally it's cheap insurance it's cheap insurance to prolong the life of the heater and make sure it's running as efficiently as possible.
I'm pretty sure I've also seen some tankless heaters installed without isolation valves, so it may be something thats not necessary for some models or in all cases, but in those cases if you do find yourself in a position where you need to flush it, that would of course make the operation somewhat more complicated.
So again in general do your research, read the manual, see what the manufacturer recommends, etc.