As suggested by bigpup, I installed a single pup on a new 4GB flash drive and bought another 4 GB to clone the multiboot drive. 

Booted the new flash drive with puppy from USB port 1 (drive 1).  Drive is automatically mounted.
Put target mulyiboot flash drive in USB port 2 (drive 2).  Drive is automatically unmounted.
Put an external drive in USB port 3 (drive 3),  Drive previously had Windows so had to be added after booting. 
Mounted drive 3 (initially unmounted)
Created a directory to accept the pudd output file - myfile.img.gz (Optional)
So, at this stage, drive 1, the boot drive and drive 2, the copy from drive are unmounted; drive 3, the copy to drive is mounted.

Step 1
Launched pudd: Menu>Utility>Pudd

Note that it is partitions and not drive information that is given although in this case drive and partition are the same.
/dev/sdc would be the source drive and /sdd the destination drive.  If either were mounted it would not be listed.
I clicked on Choose drive at this screen as I intended cloning the drive.  I did not notice that the size of the source drive exceeded the space on the destination drive.. 

Step 2

The source drive, /sdc is selected.

Step 3

I intended to do a drive to drive copy (clone), so clicked Choose _drive

Step 4

The destination drive /sdd is selected.

Got this error message because the destination drive space was too small.
Decided to do a drive to image file copy instead of cloning the drive.
Repeated Steps 1 to 3 but clicked on Choose_file at step 3.

Step 5


Step 6

Clicked Continue.

Step 7

The creation of the image file begins.  The process took a long time and there was no indication that anything was happening. 
So I took a chance and navigated to the output file and right-click>Properties.  During the display, I saw the file size increasing so was assured that the processing did not hang.
Step 8

Eventually text appeared in the yellow box, indicating successful completion.
imaging complete.

and I had the image file.