I am what you call a expert at cleaning my fuel system - not by choice!
Similar to Christian's video which I have watched a few times before, installing a port in the fuel tank was essential for maintenance. Needs to be big enough to fit your arm in there to clean the tank.
I agree with the previous posts - unless it's a full tank, it would be better to just pump out the fuel from the tank, clean the tank thoroughly, check the pickup tube for clogs, replace all your fuel filters and start with fresh fuel. If it's really bad, you may need to replace your filters again after a few sails / motoring, if there is still contaminated fuel in the lines.
If you check my posts, I just went through this again within the last few months. Last year, I purchased a electric transfer pump, did a extensive research on polishing fuel, and rigged up a fuel polishing system to save 10 gallons of diesel. System costs me $200 all in. Yea, I know, 10 gal of fuel for $200....
This year, I purchased a $30 Tera pump from Amazon - cheap but worked fine. Placed it in my tank port, pumped out my fuel and gave the fuel away to a local farmer. Wiped down the tank and replaced all the filters. Your fuel pump can get clogged too but it is a screen and difficult to twist off the bottom access of the pump.