New waste tank and grey water tank

New waste tank and grey water tank

Dear all
For two seasons now, my family and I have been enjoying a 2012 Hanse 385 (second owner) in Switzerland. We really like the boat.
The only problem we have is with the small tanks, as the waste water has to be retained and pumped out in ports. 
I am therefore planning to install a new, larger waste tank under the bed in the aft cabin on the port side and a new grey water tank under the benches in the saloon.
My questions are:
1. Does anyone have detailed plans for such tanks?
2. Does anyone have experience with how to uninstall the old, small waste water tank? (I know there have already been discussions about this in the forum, but I haven't found the exact solution yet).
Thank you for your feedback!