I had been told in the past not to get into the habit of releasing that spring for one reason or another because it causes its strength to deteriorate. And if it leaks, replace it.
Now when I want to bleed water out of that tank, I open the hot water faucet and the hot water drain on the bottom of the m/h and then open the large locking bolt on the bottom (sometimes this is a white plastic nut). (The extra water will really come charging out.) In an Atwood I think that is the bar that "bad water" chemicals attach themselves to. On a Surburban, it is just a locking valve.
That's my story and I'm sticking to it!!
Joe from Ct.