What’s the best way to clean the inside of a Chieftain Low D? What products are recommended? What tools/implements?
I clean the bore out with an oboe cleaning rod that can be picked up at a local music store which carries woodwinds. I just dip one end in warm soapy water and run it up and down the inside of the tube. Then I rinse the whistle out.
easy as that…
you could cut up your credit card, and move it through the mouth piece,
this also helps if you’re buying too many whistles 
or any ol’ plastic…
I am especially careful to observe the following regimen to the letter:
Take several gulps of Jamesons, rinsing it thoughly round the teeth and gums before swallowing almost, but not quite, all of it.
Play whistle for a sustained period in an especially ‘spitty’ manner, as if trying to target say an imaginary bodhran player, replenishing the ‘ambience’ of oral Jamesons as needed.
Collect and retain any foreign objects dropping into your lap from the whistle end as these will surely be of interest and amusement to your friends and admirers.
When the ‘rare old mountain dew’ dripping from the end of the whistle runs clear, the job’s done!
I find this effective with most whistles btw, not just the Chieftain Low D. This cleaning routine is especially useful because it can of course be accomplished during a performance or session and no-one except the bodhran player will ever guess!
You might consider this:
http://jubileeinstruments.messianic-webhosting.com/accessories.htm
Nice one, Jay-Eye.