AHHH the dreaded check valve....... depending on the year of your Jav it may be easy and it can be a total bitch to access and remove the valve. in my stratos it was take the seats out remove the base, undo the braces, and then try to get the tanks to move out ( make sure they are less than 1/3 full) you may also in the process find that stratos/jav may have stripped the check valve when installing it and also may have stripped the nut holding in the tube and valve. ( been there found that out real quick) there was soft pipe dope all around the valve and nut to seal it. I ended up replacing the tanks with 1- 50 gallon tank and bypassing the fuel tank switch and such. it is not an easy job and now I am an expert at removal and install. good luck on it also when removing the ball bearing and spring dont use a cheap screw driver as a punch get a decent punch that fits the hole or else you will end up with a very short phillips screw driver
if you need some help or advise doing it just shoot me a im or mail and I will try to walk ya thru it. also a new 50 gallon from c+o marine in tenn will cost about 140 dollars shipped to your door, if you call them ask for Steve the parts guy. Stratos sells new ones for 4-500 dollars so I would if replacing call c+o