Well I do think I have discovered the problem.
When I looked into the empty tank I could see a piece of AL tubing running spanwise along the bottom of the tank.
It would move fore and aft and was attached to a short section of hose which was connected to AL tubing and exiting the bladder at the front top.
Other end was free to move and had a red valve attached to it via a hose clamp.
Pic right tank sitting on the bottom of tank looking outboard.
Left tank looking outboard
I have Monarch aux tanks and they feed into the mains. We are thinking this might be the check valve from the Monarch tank being attached to a vent/crossover tube.
The valve and short section of tubing has obviously come free from whatever it was attached to.
The left tank has a similar setup except it is at the top of the tank presumably with the valve attached to where is should be.
I did not think the 185 with standard tanks has any crossover tube to the outboard of each tank so maybe its a Monarch thing.
Has anyone seen anything like this before?
Tom