CJ-7 Tim offers good advice. I will also further comment that the tank on a 2000 XJ is made from HDPE (blow molded plastic) and unless it is cracked/leaking, it never gets rusty inside like a steel tank would. Thus, changing the tank is RARELY needed. If the tank actually has contaminants in it (dirt, rocks, etc.), it can be washed out sucessfully and allowed to dry.
I don't own an XJ any longer, but I still think they are the best of all the Jeep products ever made. My XJ was my favorite vehicle in my 50+ years of driving.
So...I stick around and give advice.