According to C & E :
I've drained these tanks but it takes forrrrreeeeeevvvver to do. Even the
new one at the cabin. I was thinking about holding a hose connected to the
exhaust port of a shop vac around a hot water spigot, sealing as much as
possible with a rag and a firm grip, to pressurize the tank. Sounds like it
should work. Do you folks see a downside to this??

The trick that I tried most recently is similar - I used an
air compressor to "push in" thru an opened hot water faucet,
and out thru the HWT tank bottom drain line. Going _very_ gently.

While the HWT tank is capable of handling 200PSI or so, and the
compressor has difficulty getting to 100PSI, I never let the HWT
pressure get above about 10PSI.

The shop vac should work almost as well.

[I have to use pressure to blow it, because the HWT is _below_
the septic tank level, and I can't use gravity feed.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.