How add sanitizer through fresh water tank valve?

[GTSeattle]

Our campervan's (Midwest Automotive Passage on Sprinter chassis) fresh water intake for fresh or city water is a standard female screw-on hose receptacle. About an inch or so behind the intake port is a spring loaded valve that prevents back flow unless and until water pressure pushes the valve and opens it. I am challenged at how to get sanitizer into the fresh water tank. I don't have a method to provide the pressure of a normal water hose and distribute the sanitizer liquid. No funnels' tubes are small enough to fit into the passageway and press against the spring loaded valve cover. (It looks to be about 1/4 inch in diameter t that point.)

I see lots of videos of RV owner's easily using gravity to add liquid to their fresh water tanks, but that system doesn't seem to work for our camper van unit and its narrow input hole.

The installation of the tank itself is so tight, I do not have access to the overflow valve or other possible inputs at the top of the tank.

Any experience or ideas out there? Much appreciated. (No need to question about sanitizing the system - I have concluded it needs it.)

[avanti]

https://www.amazon.com/RV-Inline-San.../dp/B08F2QTQ5T

I think that there are several different devices like this available. Don't know which is best.

[GTSeattle]

I had not seen that in the hose line device. Looks like it should work.

Thanks Avanti your reply and other posts are much appreciated!

[SteveJ]

Instead of that over priced tank just pour the bleach into an empty hose before hooking it up to the tank fill and chase it in with water.

[rowiebowie]

Funnel with flexible spout.

[Rocinante]

We dilute the bleach a bit, pour that into the drinking hose and hold the hose so the bleachy-water stays there, insert that hose into the fresh tank inlet, and then turn on the water so the bleach goes where it needs to be. Works fine.

[GeorgeRa]

I use this simple device

https://www.homedepot.com/p/Powercar...1076/202560210

https://www.classbforum.com/forums/f...html#post67846