Welcome to the forum! There are many good forum members willing to provide help anytime!
With regards to your question, many diesel pusher motorhomes have ~100 gallon size fresh water tanks and as such the need rare to fill these big tanks via a "spout" and water cans (as would more frequently happen for a travel trailer with a 30 gallon water tank).
A "whole house" water filter that Spk64 mentioned is a permanently mounted "in line" filter to use when connected to fresh water in a RV park, at your home, etc. These filter look like this --> https://www.campingworld.com/culliga...3&gclsrc=3p.ds
Looking at the sales brochure for you coach, I don't see a whole house water filter mentioned so as you stated you don't have one --> www.monacocoach.com/resources/media/user/1469132246_brc_pdf.pdf
Your options for adding "water freshener" to your tank are:
1) After connecting the water hose to your coach, pour the freshner into the hose then connect the hose to the RV park / your home water faucet.
2) If you don't have a fresh water filter (using one is highly recommended) purchase the "whole house" filter with stand shown in the link to Camping World. Remove the filter housing, pour freshener into the housing, re-attached an turn on the water supply faucet.
The freshener I use is the Camco brand freshener (which is "potable water quality" bleach) --> https://www.campingworld.com/tastepu...ners-softeners
1/4 Cup of this "freshener" is all that is needed for a 100 gallon fresh water tank.
Hope you find this info useful!