One of the tools that I like to use to help clean my group is a wash bottle
like those offered at Oprhan Espresso. It makes rinsing the group easy and can get some of the grounds out that my brush can't reach. Since the La Peppina has a 45 mm group head, the Cafelat brush would be a little too big, so I use a Pallo coffee tool followed by the wash bottle. I also find a microfiber cloth handy for cleanup.
Another tool I like is the Orphan Espresso dosing funnels. I don't WDT so I like the small dosing funnel
with my Vario, but they have a taller version
if your looking for something fancier then a yogurt container. I guess if you were going to WDT, you might want a dissecting needle too. I picked one up at a science supply shop along with the wash bottles.
You can see a picture of the wash bottle and the dosing funnel in this picutre here
I even picked up a second wash bottle and Pallo coffee tool for the Nespresso Pro machine here at work, even though I try and avoid using it, favoring a hand-grinder an a Mypressi Twist instead, but someone's gotta clean the machine at work.