By keeping the slide permanently depressed, it is possible to play third position in the key of Eb minor in a similar manner to third position in the key of D minor. You can test this by pressing in the slide and playing any melody you already know in third position (e.g. St James Infirmary).
To play the E Blues scale, you only need to release the slide for one note (A natural – the flattened fifth degree). The following example demonstrates two octaves of the Eb Blues scale.
Here is a Blues solo derived from the Eb Blues scale. Notice the use of octaves here.