I use cheap chip brushes for both the tea and the vinegar. It all washes out easily with warm soapy water.
Test your vinegar solution on a scrap piece of the same wood you are using for your project. Use the same type of wood when testing. Different wood holds varying levels of tannin, which is what reacts with the vinegar/steel wool mixture. The same strength solution can make a pine board just barely brownish, while a hardwood pallet board can go jet black. It’s crazy stuff!
This is how your wood will look like once it’s dry.