On our previous boat, which was a 32' Kirie, we pulled the old 6.5 gallon (!) tank out and replaced it with a new Todd holding tank
which was around 30 gallons. It sounds huge but with 5 people on board quite often in a no-discharge zone it was nice! Had to built a new platform and glassed it in to the lazarette which was directly behind our head. Replaced all the hoses too. If you're replacing the tank - might as well start with fresh hoses! Good luck.