I spent ages working on the system, it was the little drippa one. SOmetomes it would let out all the water other times it let out none. I could never find a blockage as such just that it seemed very irratic in it's distribution. It often only gave water to the first few drippers in the line rather than all of them, just eneded up being a big hassle as I had to go down there every day to check on it anyway and sometimes they'd not have had enough water so I'd still have to water them with a can. I'm concidering trying a seaper hose but as I've not got mains pressure on the allotment I don't know if that would aid with the watering or not.