I have heard of people using a a hose clamp and a rag and mounting a lawnmower muffler on the end of a .22 rifle.Never saw it so don't know if it works well.You could always tape a plastic pop bottle on the end of a rifle like Mark Wahlberg did in Shooter.
You are looking at the old website and the wrong part. They sell the suppressor that is a registered NFA item and requires the tax stamp. Then they also sell the solvent trap.
Here is a link to the new website with the NFA suppressor listed.