Over the last few months, folks have been selling so-called "solvent trap adapters" on the internet. They're threaded dongles that allow the user to attach a commercial oil filter to the barrel of a gun. They're all over Amazon and eBay.
The folks marketing them claim they're for cleaning. The rest of us know they're a way of making improvised silencers. They're really only solvent traps if you say the phrase while making those air quotes with your fingers.
Sure, they can certainly be used to catch errant patches and other funk while cleaning, but so can a Ziploc bag and rubber bands. The device ceases to be a solvent trap and becomes a silencer once the first round is fired through it. Which is exactly what folks are going to do.
One of the companies marketing this stuff claims that the adapter is the serialized, registered part. Wrong. It's the oil filter itself. As of 1986, "silencer" is legally defined as:
any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for use in assembling or fabricating a firearm silencer or firearm muffler, and any part intended only for use in such assembly or fabrication. [18 U.S.C. § 921(a)(24)]
That means you've got to do the paperwork and pay the tax every time you want to replace the oil filter.
The ATF doesn't take an interest in cleaning supplies. What they do take an interest in is constructive possession of unregistered silencer parts. For a hapless owner caught with a gun, an oil filter, and one of the adapters, that could be a very expensive and inconvenient distinction to prove in court.
The people selling these cannot be ignorant as to how they'll be used, nor can they be unaware of the potential consequences to their customers.