As the regulars know my latestest venture was install a household commode, replace the straight drop, we love it. Now I need to add an extra holding tank for the commode.... My existing plastic tank does not have a acess port on the bottom side, where i assume the added tank would connect, Question: Is there a product made I can cut out an glue in a fitting to accept the standard cross over pipe to the new tank? What is it called?

Im assuming that bottom pipe would be in the 2 inch to 2 1/2 inch diameter? More importantly is this doable, I sure dont want to go back to the straight drop

My present holding tank when pumped out, is around 75 gallons according to the mark on the pump out boat tank Id like to double to around 150 gallons if that is doable thanks will look forward to thoughts tips