If you are burning an ethanol blended fuel, that could be the source of your problem with the carbs clogging up.
Take a look at this article:
If you are having to use ethanol blended fuel, you need to install a 10 micron water separating fuel filter in the fuel line. Racor and Yamaha makes one for small outboards.
Also, don't mix ethanol blended fuel with regular fuel that has MTBE. Once you switch to ethanol, avoid going back to MTBE fuel.
SeaFoam is fine for use as a cleaning agent and de-carbonizer and fuel stabilizer.
To clean out the old tank, just add a little fresh fuel and discard.
Good luck [img]smile.gif[/img] ,