I get a lot of hits from people searching about how to do things with the BP80. This seems to suggest several things to me:
1. People get it used online without an instruction manual. Get a PDF copy here if you don't have one. It is a big help.
2. The BP80 does so much that people aren't even sure where to begin. Take a whole day some weekend and just mess around with it.
3. Even though it is an oft maligned entry level pedal, a lot of people are entry level bass players.
I've got to say, the more I mess around with the BP80, the more I like it. It does do a lot of things, and I still maintain that a multi-effect pedal, any multi-effect pedal, is a great place to start if you are just beginning to get into the idea of effects for your bass.
Output level control seems pretty straight forward, but the BP80 has three different ways to control the volume of effects within the pedal itself. (It may have more, but I've found three so far.) So you've got your amp with a gain and volume control, the volume control on your bass (alway max this out, because you want the most powerful signal you can get going into your effect chain), and then just about every pedal you put between your bass and your amp will have some kind of level control. The BP80 by itself has three different variables that can affect the output level coming out of it, which is why I made this video:
Output level is something you definitely want to consider, especially when you have lots of pedals potentially boosting your signal along the way. Unless you actually want to have a pedal boosting your volume for a solo or whatever, it is a good idea to take some time and make sure your volume stays balanced as you switch effects on and off.