After each shot, i flush the group until I don't see anymore coffee particles coming off the shower screen. Then I wipe it with a paper towel. Usually lots of stuff comes off on the paper towel. I run the group again, then wipe again. Usually little or no stuff comes off on the second wipe, so I know the shower screen is reasonably clean.
The reason for doing this is to avoid coffee and coffee oils from baking onto the shower screen between shots and sessions. It makes a difference.
[N.B. I'm currently using an IMS coated shower screen, which behaves differently than traditional shower screens. Stuff doesn't stick as tenaciously to the IMS screen, and it can't be brushed with a Pallo or other stiff brush due to the coating. Stuff sticks more tenaciously to traditional shower screens so they require using a stiff brush.]
After each session, I do two manual plain-water backflushes with the screen in place.
About once a week, I remove the screen and screw, and put them into a one-quart Pyrex measuring cup with all the baskets and portafilters I've used. I add about 5 rounded teaspoons of Joe Glo and enough hot water from the tea wand to cover the parts. I let this soak for at least 15 minutes, then rinse the parts thoroughly with hot tap water.
While the parts are soaking, I do a single manual backflush with a little under one Pallo spoonful of Joe Glo. The Pallo spoon is about the equivalent of 1/2 tsp, so I'm using 1/3 tsp or less. I pour the detergent into a blind basket and fill with water, stirring to dissolve the detergent completely so small particles don't get caught in the gicleur. After the backflush, I let the machine sit with the detergent solution in it for about 15 minutes. Then I do a backflush with the same amount of detergent, dissolved as described above, using the GS/3 automatic backflush cycle (I think it runs 10-15 times.) Then I do a plain-water backflush using the GS/3 automatic backflush cycle. Then I repeat the plain water backflush to make absolutely sure no detergent remains in the system.
Personally, I don't believe it's necessary to run a manual backflush for more than the time it takes to build to maximum pressure, plus a few seconds. Five seconds, or whatever time the automatic cycle takes, is sufficient. I don't think much is gained by letting the system sit under max backflush pressure longer, and that the force of expelling the water is what really cleans the machine. That is, if you want to clean more thoroughly, run more cycles, not longer cycles. But I suppose it could be argued that longer cycles give the detergent water more time to dissolve coffee oils or plain water more time to dissolve detergent. LM seems to go for more cycles versus more time, so that's the way I go.
As for the steam wand, I wipe it with a damp cloth after steaming, then pulse the steam to clear the opening. At the end of the session, I fill a cup or pitcher with water, insert the wand, let it steam for a second or two, turn off the steam, direct the wand to the drain box, and pulse the steam. Then I repeat once. I do this because I've read that milk can get sucked up into the steam tip when the steam is turned off. So I steam water in the hope that water will get sucked up into the steam tip, will mix with any milk in there, and will be expelled when I flush it into the drain box. This all may be wishful thinking on my part. I still have to remove and clean the steam tip (a Spro-Knife) periodically, but possibly less often.
[End of Message from the House of OCD