Berthound force 10 won't self fill

[bandit]

First time I've used it tonight as far as I can see all taps right way, over 50 l in tank but I can't get any suction. Am I missing something simple [emoji848]?

 

[Ormond]

Check all the connections on the suction hose are sealed and not drawing air ....rubber seal is in the camlock fitting if it has that connection

 

[bandit]

Ok had tea and thought, try again and it sucks!! [emoji10]
I presumed the suction pipe was the top one, no idea the purpose of it otherwise