i'd generally advise against using the single basket - your much better off using the double as it gives you more wiggle room to get the shot right, also who drinks a single shot coffee? really?
You're basically looking for volume and time - get the right volume in the right time and your laughing, not sure what controls the sage gives you but your looking for around 30ml in 25-30 seconds (60ml in a double basket)
You can fine tune this in three main ways:
- the grind
- the pressure, pressure should be about 9bar, but again you can play with this.
- the amount of coffee - your looking for about 18-20g for a double.
essentially your best fixing pressure and weight of coffee at 9bar & 18g then playing with the grind. If you're finding the coffee too strong you can increase the amount and decrease the grind slightly, or just play around generally (there are loads of threads, experiments, blog posts etc about it)
In theory swapping between single and double baskets shouldn't do anything, but in reality i'd be surprised if you got consistent results, MTFU and drink doubles
Black plastic thing in the portafiler (handle) is probably an aerator to agitate the coffee and give a better looking crema, if you can take it out (non-destructively) I would do... its lying to you