I have tried a few different ways to clean the inside of the Way/Support tubes.
I found the way that works best for me with stuff I had (Laying) around the Shop in the pictures below.
Also included in the pictures,
I am going to use the same stuff,
that Member (AllenH) used,
Because I have had this for several years and was going to use it on a Truck Project.

It is from Eastwood and in a few pictures below this.
I used a Miter saw to cut a Slit in some 1/2" Cpvc pipe.
This slot will be used to insert a Scotch Brite in it and use as a Flapper
So, I cut 3" off of the 6" x 9" pad.
6" x 6" ruffly

I used a coupler to join 2 pieces of pipe together to reach the end.
I drove a 1/2" drill inside the Cpvc (Hot Water) pipe for the driving force.
I also have been Over thinking this maybe.

I cut a Tube of this same Cpvc to hold the spray tube straight.
Can Nozzle end.
Here is The Business end.

This is the stuff I am using.
I had this roller setup from a Production line that was gave to me.
I freed up two rollers to make a spinning platform to spray this paint on the inside of these tubes.
Here are the plugs that I am going to use to cap the tubes.
I got them from Ama Zon and I had to do modifications too.