Hello; An interesting thing is regular water changes (WC) are sort of a gospel among aquarium keepers. Some with chloramines in the treated water use agents such as PRIME, SAFE or something similar and send tap water straight from a tap into a tank. I have some of the stuff on hand myself. Yet in this thread for post after post a high degree of concern over the potential danger of filter parts being rinsed with that same tap water. Not soaked in a bucket of the tap water to be sure. Rinsed and allowed to drip off. The sponge like media is squeezed to remove as much of that dreaded tap water.
OK some small amount of the tap water will cling to the rinsed parts. Can it be so much different that a 50% WC to use some PRIME or SAFE? In fact, I tend to do any filter cleaning at the same time I do a WC. Still even if the filter is cleaned on a different schedule a small dose of SAFE ought to take care of the dreaded residuals.
Still worried, put some PRIME/SAFE in a bucket and run tap water in that. Drop the rinsed filter parts into that bucket for a few, then reassemble and be on your way. Probably other ways to get around the worrisome issue. I have mentioned some already.
A few have ventured into the benefits of a clean filter/ filter media. The dogma of lightly swishing dirty filter material in a bucket of also just siphoned out old and still dirty tank water and then putting the gross and only minimally cleaned filter stuff back is use is not one I follow. Not sure what disaster I am supposed to be courting, but I have been cleaning my filters with a hose for a few decades now. I do not do a deep clean every month. Usually replace the "pillow stuffing" with new and check the reusable filter parts to see if they are clogged up. I only go the hose and deep clean route when needed.
The issue remaining is what % of BB colonies are lost. I do not have a number to throw out. As stated before there is not a biological mechanism I know of that restricts BB colonies to only filter media or even only filter parts. My take is any surface with a bit of flow touching it can hold BB colonies. I , the last few decades, tend to run a low-density stocking in my tanks. I get that BB adjust their populations to their nutrient source available (ammonia). I also get BB are not rapid reproducers as some other bacteria are. Again, if ammonia levels are a concern there are strategies we can use. We can get short term ammonia spikes simply be adding a bio load of new fish or not discovering a sizeable dead fish for a few days.
A few times I have had to break down and sanitize entire setups. Soaking tanks, gravel filters and all other equipment in a Clorox solution. Even with a lot of rinsing some Clorox remains. When I set the tank up again it gets dosed with SAFE/PRIME or the like. Seed the new setup with BB from another tank to get it up and running. Just do not see the need for all the hand wringing over using a hose to clean a nasty filter.