Purwater FHT-34V water filter (Cuno)

I recently purchased a house which has a whole house water filter installed (Purwater FHT-34V). I changed the filter which looked like it hadn't been changed in years. The filter has a valve in the lid and I am looking for help in understanding how to know when the filter is in "bypass"' "off" and "filter" settings. There is a little tab on the lid which may or may not indicate the setting. When I changed the filter the little tab was over the "bypass" setting and water was leaking out so I had to shut off the main water valve to change. Just curious if anyone has had experience with these filters as I haven't been able to find any manual. Photo attached showing way I found filter housing.

The picture shows the system in bypass mode....which means water will pass thru the pipe without going thru the filter housing.

Off, means, well...off. No water shall pass thru, basically becomes a shut off valve.

And filter means water will pass thru the filter. Whatever that tab is pointing to is the setting it'd on. To change the filter you want it set to off, you will still get a bit of water if there's no shut off valves on the other side

Thank you very much for your assistance!

I have the same situation as the other person in this post. I moved into an old house that has the above model housing. Would you recommend changing the entire housing, not knowing how old it is? Also, I'm confused to the type of internal filter to use. There seems to be different ones for very specific needs (sediment, chlorine, etc. Isn't there one filter that does it all? Do they fit within each other to create different stages of filtration? Are there better filtration systems that you can recommend? If it helps, I live on Long Island, NY. THANKS!

I also have a bypass filter model FHT – 34V when I put it together it still leaks I believe I need the black rubber washer is that still available??