Domestic hot water storage tank maintenance?

Yes, I should read the manual, but I thought I'd ask here first anyway.
I have a domestic hot water tank that is heated by my oil fired boiler through a separate 'zone'.
Do I have to drain off the the bottom of the tank? It hasn't been done yet for the 4 years of its life.
It's well water, but we have a filter and softener.
Thanks.

I would, just to see what comes out. Why not?

If it's clear, then don't worry about it anymore.

Yeah, I guess you're right.
Maybe I'll see if I can find the manual too, before I start draining things.
One gas hw heater I had with city water that came from wells had a lot of iron on the bottom.

If yuou have filter and softener, then you should have minimal tank deposits. Before we got our softener, the finned hx coil in our DHW tank got really calcified. I put 10 gallons of vinegar in it, heated it up, and let it sit for two days. You wouldn't believe the crud that came out.

As previously mentioned, go ahead and run a gallon or two out the bottom to see what you get. Can't hurt anything.

nf,
Is that something to can inspect visually?

If you could get your hands on one of those fiber-optic laproscopic surgery doohickeys, yes. Otherwise, no. The symptom is that it takes longer for your boiler to heat the hot water. If you have one of those infrared thermometer (these things are like crack for pyros), you could measure the HX inlet and outlet - less drop means a less effective HX. I might even tell you what mine shows next time I build a fire.

I don't have any experience with indirects, which is what this sounds like, but a conventional hot water coil in a boiler can usually be unbolted and removed for inspection without too much trouble. Even better, if there's a well above the coil, which is often the case, you can remove it and inspect the coil with a flashlight. Depends on whether the coil is immersed in boiler water or potable domestic water, I guess. If the latter, then the fins would be all caked up with lime. If it's a coil without fins, the same approach should work as well, assuming you can easily get a look at it.

Not on mine - (SuperStor) all welded together. The HX is a finned stainless coil in the tank with the fins on the potable water side and the boiler water inside the pipe. The only access to the tank is via the hot and cold water connections, and those may have internal baffles to promote stratification.

What, no drain?

No - just a faucet teed off the cold water inlet (I think - it's all wrapped up in insulation at the moment).

I have one of those doohickeys.