another vacuum problem

[fatmoggy104]

Im looking after a in ground pool it has no vac outlet so i vac from skimmer the problem is if i close bottom drain pressure go straight to red but if i crack it open a little vacumming is poor same if i close eyeball valve pressure goes straight in the red and open it a little vacuuming poor
only time vac works properly if i move valve to waste. What am i doing wrong.