the fuel tanks are made by Acerbis from a type of nylon known as 6/6, aka Polyamide 6, or PA6. Nylon 6/6 absorbs water, up to 8% by weight. The water molecules displace the nylon molecules, deforming the nylon molecular matrix. Additionally, the increase in spacing between the nylon molecules decreases its stability and allows the nylon to move.
Ethanol is hygroscopic and draws moisture from the air. This makes it heavier and, when there is sufficient moisture content, phase separation occurs at the bottom of the tank and the water/ethanol separates from the gasoline. The released water is absorbed by the nylon tank.
The nylon can dry out again if no/limited moisture is in the tank, decreasing the swelling.
Sea Foam contains isopropyl alcohol which solubilizes free standing water in gasoline. Ethanol does the same.
When ethanol containing fuel reaches a saturation point, the ethanol and water phase separate as distinct layers at the bottom of the tank (an ethanol/eater mix and a separate layer of water below it). Adding isopropyl alcohol can solubilize the water, but now you have even more alcohol in your fuel.
Exacerbating all of this is that the amount of water ethanol can hold in gasoline before phase separation occurs is temperature dependent. A drop from room temperature to 20F decreases the amount of water the ethanol will hold in solution by over 30%.
The only real solution is avoiding ethanol laced fuel.
'15 BMW S1000RR, '10 Streetfighter S, '07 1098S Tricolore, '05 999