Lots of turners use a sanding sealer jar with the brush inserted through the lid. This is very handy because the sealer doesn’t evaporate or get full of chips. The brush stays wet and ready to go. Here is an easy way to fit the brush and keep it rigid and with an airtight seal.
A waterproof cable gland from an electricians supply store is intended to make a seal where a cable enters a box, and consists of a flanged screw fitting with rubber sealing washers and a compressible rubber sleeve that will tighten down on a wide range of sizes. They cost very little. The brush must have a cylindrical dowel handle and rust-proof bristle holder. I found some cooks’ pastry brushes that are just the job. You can get them cheaply from Amazon, and the glands too.
The only tricky bit is making a neat hole in the lid of the jar. If the lid is plastic, you have to go gently with the drill to avoid cracking it. If metal, start with a small drill and then file the hole to size. Don’t attempt to drill the hole with a large drill bit. It will grab the thin metal when it cuts through and damage either the lid or your fingers, or very likely both. It is essential to clamp thin metal when drilling it if you value your fingers. Sandwiching the metal between two bits of board would help prevent grabbing and distortion. This would be the best approach, but the lid flange makes it difficult.