I am glad you found some additional discussion of washing soda Kritts. Jo mentioned washing soda crystals a while back and I had no idea what it was. She evidently uses it to clean her drains as well. So I started this thread which has a link to a UK site where washing soda (or crystals) was discussed) by forum members:
Sharing a smile
Here's where Jo mentions using this product in drains:
worms pulled from my face, nostrils, and hands
Now I am wondering if the Arm and Hammer washing soda has the same ingredients as the online UK product. I have just purchased a box of Arm and Hammer (this product has suddenly appeared on the shelves of groceries in my area when just a few months ago there was none to be found), but it does not suggest using it in drains and says not to use it on anything aluminum. I am glad Jo has posted more information on this thread on how to use this type of product in the washing machine to better effect.
The Dri-Pak Soda Crystals have: sodium carbonate decahydrate, magnesium hydroxide, and silica while the Arm and Hammer Product is 100% sodium carbonate. Guess this could make a difference as to how safe it is to use in other ways.
Just did a search on Arm and Hammer to clean drains (guess you can you use it on drains though I did not find this information on the US Arm and Hammer site):
https://www.wegmans.com/webapp/wcs/s...ProductDisplay
Traps and Drains: To help keep traps and drains open, dissolve 1/2 cup per gallon of warm water. Run hot water down drain, add Super Washing Soda solution, then flush with hot water. Do not use for blocked drains.
Just found this from the Canadian Arm and Hammer site, a pdf file which lists all the secrets about using this product:
www.armhammer.ca/en/ArmHammer_Secret_Tips.pdf