Push the boat out and get yourself a £2 bently brush from asda 
I use these and I think they do the job fine. I've not had any complaints from them that I can think of? I've got about five spare brush heads in the shed; it takes me longer to find the right size drill bit than it does to drill the two holes to convert them into a WFP!
Nothing at all wrong with Bentley brushes, I have a superlite brush on the Harris pole, and a Bentley on the SL2, both are swiveled and do the same job.
The Bentley has jets on Algarde stalks with micro watering jets from B&Q stuck down the end.
Having jets on stalks level with the end of the bristles means the water doesn't have to find it's way through dirty bristles, so easy to rinse on the glass.
Drill a 5.5mm hole through the brush stock, push through the 6mm Algarde hose, stick the 2mm jet into the Algarde, pull back until level with the bristles, and connect the other end to your Y piece. Job done.