When you pull the black tank lever to empty is it normal to get a small amount of seepage from the pipe to valve coupling,the one immediately after the open / close valve?
I have changed the pipe coupling but still get a slight leak.
If it's leaking from the bayonet fitting on the sewer hose, then just change the bayonet fitting. The o-ring is probably worn out. If it's leaking from a cemented joint, then the repair is a bit more difficult. If it's leaking from the valve assembly, then you can replace the valve.
Thanks for your reply, is the 'O' ring on the coupling at the start of the waste pipe or on the black plastic valve?
I replaced the pipe and coupling just a week or two ago, the 'leak' isn't severe and appears to be worse if the flow along the pipe gets restricted by a bend.