I have recently jetted a couple of brushes using 6mm Algarde hose, these jets are level with the top of the bristles so the water is not having to fight it's way through when your scrubbing.
Drill a 5mm hole where you want the jet to go, screw the Algarde through the hole, it's not easy as the Algarde is 6mm diameter.
To make the jets you need a thick drinking straw cut up into 6mm lengths, fill the piece with Araldite and push a waxed darning needle through the tube and the Araldite, when the Araldite has gone off pull out the needle. you now have a jet about 6mm in length to insert into the end of the Algarde tubing.
I used a 10" length of Algarde for each jet. connect the ends to your Y piece and pole hose, away to go.
I find having the jets very close to the glass works a treat.
Screw the Algarde though the brush from the side with no bristles, you will never get it through from the other end.
You may find it better to have a piece of polystyrene to rest the jets on when your making them, the needle will stay upright making it easier to get the hole in the centre.