Above is a picture of my dip tube setup. It is fairly primitive but works well.

There are three tips that may be of interest.

1. There is always a problem of the varnish rising in the tube when the rod is lowered into the tube. I take the cap off the tube and slip a 4 inch long piece of clear plastic tube over the outside of the dip tube. The clear plastic addition goes over the dip tube about 1 inch and extends about 3 inches. As the rod is lowered into the tube the varnish rises into the clear plastic section, rather then spill over the side. It also enables you to see when the guides etc. are nearing the top of the varnish and you can get ready to stop the motor. This enables you to keep the varnish level at the top of the tube when not in use. If the varnish level drops a little after a rod is dipped just drop a glass marble into the varnish and the level will rise again. The marbles also stir the varnish by inverting the tube a few times (with the cap on of course).

2. I used a simple BBQ turner motor. It is battery operated and has a simple on/off switch. I do not have it connected to a pulley but to a brass rod about 12" long. I used brass because I had some but wood or steel would do as well. The rod goes into the turner motor (the end was filled square to fit in) at one end and into a round hole in the wall at the other end. I experimented with different diameter rods until I found the diameter which when turned by the motor resulted in a withdrawal rate of about 3" a minute. The end of the string was attached to the rod with a touch of super glue and the string winds along the rod as the motor turns it. This provides a constant withdrawal rate. (Ray Gould's suggestion) The string goes to a cup hook at the top of the enclosure above the center of the rod then to a cup hook above the dip tube.

3. The third tip is to set up your motor outside the dipping enclosure, not inside like mine. It will make it easier to turn the motor on and off if you have a plastic curtain you pull across like I do.