I don't have a 3401, but in the factory tour, I saw that many of the tank formations were all very similar among the different floor plans.  On ours the front bathroom black tank and grey tank are actually side by side and run long ways front to back with the black on the left and the grey on the right side of the RV with a large pipe to the outlet from the black and the grey has a smaller size line into the side of the outlet.  with ours we have a 1/2 bath and the sink and toilet both drain into the same second black tank and this tank actually sets above the other two tanks and runs side to side with the plumbing swooping down into the outlet.  In our wet bay the black tank flush goes into both black tanks simultaneously.  Not sure if this helps, but please ask more questions if you need anytime!

We have a 2015 39mb. I've attached a drawing of the holding tanks and related plumbing that we got from the factory. We do have a drawing for the holding tanks and a trouble shooting guide for the level ups in PDF files, but we cannot seem to attach them to the post. Does anybody know why you can't attach a file to a post? 

Thanks for the help

@sdeserano Stan, you should be able to attach files using the commands just below the comment box. There is a "My Media" and "Attach Files" above the "Add Reply" button. Try that.