Join Date: Sep 2013
Location: South Devon
My Motorhome: Bessacarr E725
Thanked 161 Times in 140 Posts
It sounds like my filter which isn't surprising given our vans are almost identical.
Assuming your pump is under the floor by the wardrobe, you could undo the screws securing the pump to the floor and move the whole shebang sideways to bring the filter into reach.
The filter casing twists apart and seals with an O-ring.
If you can't access it to dismantle it, I would suggest smearing a bead of vaseline into the joint and that should stop air leaking in.
I'm daft and proud of it.