I replaced primary filter a few times on my 04 Signature with a DD60. There is a valve at the secondary filter on my coach. I just close valve, remove primary filter and fill new filter all the way to the top thru small holes (takes awhile) then install. Open valve and DD60 starts right up. Never had a problem......
2004 Monaco Signature with a Detroit 60, Vorad Radar, Samsung Fridge, Induction cook top, 2020 GMC Denali