Muting is one of those unglamorous but important techniques that's easy to overlook. Unwanted string noise is horrendous though and something you should work hard to eliminate from your playing.
I have another muting lesson that you can study: Bass Guitar Lesson – Muting Unwanted Noise.
This one is more specific to slap technique, where it's a little more difficult to control the strings. It actually came from a question I got from a subscriber:
I play a 5 string bass and I am really into slapping. But for slapping the muting is very difficult. I searched a lot on YouTube for that, but I found nothing. What is the easiest way to mute the strings properly on a 5 string bass for a clear and crisp slap tone ?
If you want a question answered, get in touch!