It's been a while since the Altered Scale was discussed in these pages--44,640 minutes, give or take a few. You may have forgotten some of what appeared here last month, and I have a way to help that. One trick for remembering the Altered Scale is thinking of the Myxolydian #4 scale built a tritone away from the dominant chord in the progression:

These are exactly the same notes, just starting on a different pitch.

With Myx #4, you don't have as many altered pitches to remember. It's just a basic dominant scale with #4. Clearly not the same as keeping track of b9, #9, #4 and b13. Using the substitute dominant brings some nice melodic contours to mind that wouldn't otherwise be obvious:

In the following example, the Gb Myx#4 is used as an umbrella over both the G-7b5 and the C7 alt. It sounds good becaus the notes not belonging to the underlying G-7b5 chord create a lot of tension. It won't keep you dry however.