You should only have one pipe for the draining of the tanks...gray and black. So in effect, it is already "T"'d together. You will want to drain the black tank first, then drain the gray tanks. This helps wash out any "stuff" from the black flushing.
Congrats on your new purchase, and welcome to the wonderful world of RVing!
Ed and Sharon
2010 Wildcat 28RKBS
2011 Ford F-250 XLT, 6.7L PSD
Ride-Rite Airbags and Airlift wireless remote compressor...nice!
I thought I was wrong once, but I was wrong!