No it's not that simple. Using the stock tank for vegi oil - you said bio and thats al together diferent - is a no-no. And heres why. certain metals, like steal, are known to react with vegi oil, free faty acids, moisture, heat and air (all of which are present in a tank of VO) creating a skin like crud (i call it friut rool ups) in the tank when using metal tanks. These fruit rool ups will grow in your tank (literally grow) and eventually let loose and then it's filter city. Don't want to do this. Aluminum does not have this same reaction with those elements so an aluminum tank is ideal. Copper has the same reaction so don't use a copper heat exchanger inside the tank for a heated fuel pickup line. For the PSD, the best and simplest system for converting your truck to use vegi oil is the "
vegistroke" kit. Click that link and you can check it out. You can buy this kit, and an aluminum tank (plastic wil work too but not recommended because of the heat) and install this system and within a year, it has paid for itself and your makin money. I have one and like it very well. If you have good oil sorces, figure out an easy collection system and go.
Good luck and ask more questions if you have them.