cleaning gas tank

[fencepost_79]

hello everyone. i am new to this website and this is my first post. i am the soon to be owner of a 2007 toyota yaris. it is the sedan type , not a hatchback. the lady i am buying it from says everything is good and runs. this was just a backup vehicle for her. the only issue is that it has been sitting for 2 + years. also, a hail storm broke out the back windshield (but thats irrelevant, at least for the time being). so im just asking your help/tips/general overview on the steps to take in order to get the bad gas out of the tank and preserve the fuel pump assembly unit in the process. I plan to work on it within the next few days. I am a diy/shade tree mechanic. and i cant afford to have a shop do this. so yall's tips/advice is appreciated
how do i depressurise the fuel system?
is that necessary? (I do not want to suck up any of the bad fuel/debris in the fuel pump before i clean the fuel tank.)
im thinking logically that i need to disconnect the lines and electrical connector first (under the seat) before I drop the tank.
what is your suggestions on cleaning the tank?
Further..I want to test the pump with my multimeter.
any advice/tips/suggestions..anything regarding this procedure I appreciate.
Thanks!