You're probably better off asking this question in the Washington State forum, where local users who are more familiar with the system can help you in detail.
But from me being on the other coast and looking at it, the first thing I'll say is you only have to worry about the Control Channel frequencies, the ones in red and blue. Forget about the rest of them.
I see 15 different sites listed for that system, which means it most likely covers a pretty wide area. What this also means is that most likely not all talkgroups are broadcast over every site, that would be a waste of resources. There's no reason to have Seattle PD broadcast on a tower 50 miles away, for example, when that talkgroup is only relevant within the city limits.
So what you need to first do is figure out what sites you are closest to and can receive, because unless you live on a big mountain right smack in the middle of all 15 sites, you're only going to receive one or two or maybe three of them. So put the scanner in Search mode and enter each Control Channel one by one (the red and blue frequencies). You'll know right away if you've found an active one within range by the noise it'll make (sounds like a low pitched machine gun). Make a note of each one you receive and how well you're receiving it, and what site it belongs to. Once you get through them all, you should have a good idea what sites you can receive reliably.
Once you've determined that, you can plan out how you're going to program the system into the scanner. The bottom line is that each bank can only hold one system OR site. This is very important to understand, because a lot of times it simply says "One trunked system per bank", but that's not entirely accurate. You're actually limited to one SITE per bank, even if there are multiple sites within the same system.
So let's say, just for example because I have no clue where you're located in relation to any of those sites that are listed, that you wind up being able to receive the Control Channels for Site 001 Seattle Simulcast and Site 006 King County/ValleyCom Simulcast. You might need two banks to scan both sites. In the first bank you'd program the 868.1750 and 851.4125 Control Channels for Site 001, and in the second bank you'd program the 851.8125, 867.8625, 868.4250 and 868.4500 Control Channels. You don't need to program the rest of the frequencies, the scanner will find them on its own as long as you have Control Channel Only enabled in the scanner's settings for each bank. Then of course you need to program in the talkgroups you're interested in hearing, and hope that they are simulcast over the sites you are able to receive clearly.
Now of course, maybe you get lucky and they simulcast every talkgroup over ever site, in which case you'd only need to pick the closest site, program those Control Channels, and program the talkgroups you want to receive. Again, I'm not at all familiar with that system, so you'd be better off asking for the particulars in the Washington State forum.
Good luck!
PS - You might want to make sure your BCT8 has the latest firmware. It doesn't look like that system has undergone rebanding yet, but it will eventually. You'll need the latest firmware once it is rebanded in order to properly trunk track the system.
BCT8FirmwareUpdate < UnidenMan4 < TWiki
Didnt get anything at my house when adding the trunking system that sounded like the machine gun like the other tunk systems i have around here that i can listen into. Didnt pick up anything when in king county either. So i might just have to take a trip down with the frequencies all printed out and pull over on the side of the road and see if i can get anything. 
