VPI 16.5: How Hard to Brush???

I just hold the brush in place with some pressure, but no way to measure pressure. In addition, before this washing step I use an ordinary Audioquest carbon fiber dust remover brush simply held in place, twice or three times, for two or three rotations each time, on an ordinary turntable since this seems to eliminate a lot of particulate matter which can make the VPI suction device accidentally rub abrasively against the record. This extra effort is for old records from library sales, thrift stores, tag sales, etc. which can benefit from multi-step process. There are many record cleaning solutions available apart from the one included with your unit. I'll let others recommend, and you can check archived discussions.

Generally, when using any brush for cleaning into grooves or pits, it is counter-productive to press down to the point where the bristles bend significantly. The tips of the bristles are what will get down into the bottom of the grooves, and when they are bent, they don't do as well. Keep the bristles fairly straight, and you'll do fine.