De Dietrich diswasher rins aid ?

HI,
I have a second hand De Dietrich DVF111JU1 diswasher I cannot fill up with rins aid. It overflows but the light is on that it needs re-filling. When filling the rins aid compartment looking at the little window on it I cannot see that anything would run in to it. Glasses come out cloudy and everything has a salty taste. Using 3in 1 tblets slightly improved things but stil not how things shoud be.
Many thanks