Help draining Black/Grey tanks

[JPz]

I have a brand new Montana High Country 334BH. This model has an extra 1/2 bath in the rear bunkhouse. I did not get a very good run thru on this from the dealer (I assumed it would be similar to my old 5th wheel). I simply do not know how to drain everything. There is a outlet to hook the sewer hose to around the middle/front of the unit then a second one at the rear. In the Water center there is a black and a grey valve, a few feet away from that by the first sewer connection is a small door that leads to another valve. Then, there is yet another valve on the frame, behind the slide near the rear sewer connection. We took it out on it's maiden voyage recently, when it came time to dump, we pulled up to the first connection, pulled the grey in the water center, then the black, then the extra grey one on the frame (I assume is the Kitchen), when finished, pulled up to the rear sewer connection, once again pulled the grey and black in the water center, then the last valve on the frame near the rear. When all was completed the panel read 2/3 full on black2. Is this the correct process for this unit and how do I clear the black2 tank? This is quite a setup, and also why are there valves underneath, these are very uncomfortable to get to when dumping.