sounds like, in addition to other ideas, your friend ought to replace the drain valve on his new WH before it is installed with a ball valve. shopping list:

3/4" pipe nipple, to fit
3/4" threaded ball valve
3/4" MPT to GHT brass adapter
brass GHT cap (so if someone kicks the valve lever you don't have a basement gusher)
pipe dope or tape

then flush out the tank periodically... standard recommendation is every year but if it's gunking up that bad might want to do it more often. Turn off breaker before doing so so as not to burn out elements (or turn off pilot on gas so as not to stress tank heating it dry)

with a ball valve you'll get much more flow than a boiler drain so hopefully that will carry more sediment out, and in any case won't stick/fail/need replacement for the life of the WWH

To make it more convenient to flush regularly, leaving a dedicated garden hose next to WH long enough to reach laundry sink is a good idea, can be length of an old patched outdoor one, you're only going to use it every now and then anyway.

I've seen recommendations for a curved end dip tubes to help keep sediment from accumulating; I don't know if those help or not. Makes sense in theory though.

good luck,

nate
nate