I was able to hard plumb the gally tank and the grey tank together on my 30KFB. The TT already had a dual valve drain (black & grey) in the back. I simply had to get a pipe between the two.
I really didn't like having to drain the galley then pull up to drain the grey and black tanks AND connecting the two gave me a bunch of peace of mind from a capacity standpoint. We can camp a week now without filling the tanks.
Bryant, Kristin, Elijah & Joseph
2012 Puma 30KFB
2006 2500HD Duramax