Another way is to use point filters. There are several ways to do this, but simplest, I think, is to click on the pipe, grab the grip you want to move in plan view, type in ".Z" (note the period first, then the letter Z). The command line asks you to select the Z reference elevation to use, so snap once more to the same grip edit, then snap to your new location. In this manner, you will retain the exact Z elevation that you began with. Now, whether or not that is the final elevation you want is another question, but at least it won't snap to zero, forcing you to edit your pipe elevations evertime you grip edit one.
As Andrew Ingram mentioned earlier, moving the structures where possible is the best idea as the elevations stay constant without having to use any tricks like point filters, etc.
