Tank Drain Connections - 1976 Sovereign Center Bath

[NTVB73]

Hello Everyone,
I'm in the process of replacing the axles, and all of the running gear, on my 1976 Sovereign International Landyacht Center Bath. Well, once I removed the axles I thought, hey I should remove the belly pan and clean up the whole frame, instead of just doing the area in the wheel wells. I should also mention that due to bad or no winterizing by a PO the copper plumbing needs to be redone with PEX, so you see how one thing leads to another. Remember, this started with replacing the axles. Anyway, the second step in my service manual, under Main Waste Tank Removal and Replacement simply states 2. Remove Drain Lines. The interior of my Sovereign is immaculate so I do not want to rip up the floor. My question is, where do I access the drain lines for the black and grey tanks? Can this be done without removing the floor? From the reading I've done, I know this has to be done from the inside, somewhere, but I can't find any specifics. If I disconnect the toilet and flange, the shower and lavatory drain, and the galley sink drain, will the tanks be free to be safely lowered?

Thanks for any wisdom you have to offer.
Nick