NEED FUEL SYSTEM HELP / also deck height adjust info

I inherited a Craftsman GT6000 , model number 917-257720 , serial number 032494C that has been sitting outside for several years . It will not start with fuel in the tank , but will start with ether . I noticed that the lens is missing off of the in tank fuel guage/cap, so i'm sure it has water in the tank ; my question is what do i have to do to remove the fuel tank ? I am also planning on replacing all fuel lines and filter as well , they appear to be original . I also have noticed that the deck height adjustment knob will not turn , any help on the mechanics of this system would be great .