Rpatrick its about 11 gallons bigger, no just kidding, Kevins right, but you can change it,but it is a messy and really stinky job, just make sure if you do it to wear the proper safety gear, you don't know whos been going in there, also measure your spot where the tank is and if the bigger one will fit, where the fittings are, and if you can get at them, and if you do change it,think about the hoses as well,if you put on new hoses (white ones) to get them on/off the fittings use a heat gun to soften the plastic hose and use some grease/vaseline on the fittings when reinstalling also good workgloves because that hose stays hot for a long time, trust me I know I have done one and thats all I want to do as the owner stepped down onto the tank and broke the fitting, there was CRAP everywhere, so PUMPOUT/FLUSH/PUMPOUT/FLUSH/PUMPOUT, to get out as much a possible, use good sealers on the threads and double clamp so you don't have any leaks, good luck Myles :-)