Chuck;The ethanol swelling is a dwelling issue. Time spent in the tank to be absorbed by the plastic. If you do a "swish-and-drain" there should be no issue. Further, you could use a long handled soft brush to aid loosening the dirt. To finish, air dry on low with a standard hair dryer.
Not in the US (I'm not sure what area we're talking about here anyways) - In the US they have to be metal. That solvent is fine with plastic anyways. You leave the plastic fuel pump in when you do the treatment so it can't be harmful.Plastic tank, I'd be careful, probably just a good detergent, some cloth on a piece of wire, obviously remove the fuel pump for better access. Then rinse with clean fuel. Anything else that stays behind is the filters problem I recon.