Personally - and I state this as a "what I do", not necessarily "what to do" - I scrub after every use and then backflush it once a week with just water, backflushing with Cafiza once a month. I use it about as much as you do.

 

I found this link that explains the operation of the three way valve, and the reasons why backflushing is essential.

http://home.surewest.net/frcn/Coffee/3way/intro.html

My understanding is that backflushing, particularly with plain water, causes no problems, and do it at the end of each day on my Rocket. With E-61's, there is an issue with using a detergent, as it removes lubrication from the lever mechanism and causes premature cam wear, but there's no such problem with the Silvia. I use a detergent about once every three months, and despite regular plain-water backflushing, and weekly removal and cleaning of the shower head, it's amazing just how much junk comes out with the detergent.

 

I back flush just with water after a shot if I might not have another or if it will be a lot later. Don't want the old grinds burning on the shower head.

I've used purly once since owning which was before Christmas but it's hardly getting used anyway

 

I do exactly the same as cjbailey and descale about every 3 months but I also use filtered water and have another filter connected inside the tank. Every couple of months I take the shower screen off and boil it and the other bits in a water cafiza solution.

Edit: Just read the link that Vintage posted up. Very good read and explained a few things I was unsure of... Now off to backflush my machine

Going to do at least a water one after every shot now. Must move sink closer to my machine

 

Just done a backflush with cafiza and removed the showerhead for the first time. Neither were hugely dirty but at least it keeps the machine maintained.

Thanks for all the replies.

 

I normally set aside a few hours once a month on a Sunday to descale, backflush and generally clean my machine.