Engine stalls, runs rough after topping off the fuel tank

[cruz'r]

Hello Maxum owners, this is my first post. Just acquired my 2000 2400 SCR about 2 months ago, was able to take it out on the water only 2 times. I was so thrilled the first time I took it out, engine running perfectly fine, went around Bainbridge Island (sorry... if you're not from Washington you may not have any idea where that island is) for 2 hours mostly running high speed. Second time I took it out, decided to top off the fuel tank at nearby marina, since then the engine (305) started running rough, stalls for I don't know what reason. Expert at West Marine says, I may have stirred up all the sediment at the bottom of my tank. Bad/contaminated gas? How to siphon the gas out from the tank? Thanks for the help.