Problem with using Water Fed Poles on CCU

So I’ve been cleaning down my windows and frames on CCU jobs using my wfp.

This is in place of using huck towels or scrims to detail - which can save a lot of time.

Though it expedites some of the work - there is often a gray strain on the frames from the concrete render. This rubs off with a microfibre cloth without too much trouble - but it’s an extra detail I don’t care for.

Any creative ideas on how to prevent this?

I thought I might experiment using hot water and using more water with minibore for a good rinse - but I think somebody might have a different answer.