Well, I haven't tried it, but here's a curezone post from someone who does it -- my comment is perhaps to try it with less epsoms per that amount of water (in other words, try it with a more diluted mix, not so strong), because elsewhere there is a story about a child actually dying when the parents used a too-strong mix of epsoms in the child's enema.
Also, the person who posted at this link says she/he thinks epsoms in the enema can stress the adrenals, just like they can when taken orally, so the enema route may not be any better for your adrenals. But for what it's worth, here's the link: