No. Since the ATF has classified solvent traps as accessories, purchasing a kit is no different than buying any other commercial product online.
Yes. A suppressor is a controlled item also an NFA (National Firearms Act) item. Federal law requires that anyone who does so still register the device, and submit it to a background check before construction.
A solvent trap is a device that is designed to attach to the threaded muzzle of a rifle in order to capture solvents, and / or fluids used to clean the rifle.
By adding a bullet exit hole it can function as a suppressor which necessitates Form 1 submission and a paid tax