Well, you might wanna take a look at my study blog as leech squashing is what I’ve done most over there. I mainly use the Item Inspector, Self-Study Quiz and the Shin Wanikani Leech trainer. You can find links to them all on my blog as well.
I try to be consistent about going at the leechs. Like one or two sessions per week, however much I can manage. Just to keep the numbers down.
But, I also do bigger review sessions from the Item Inspector (quiz entire table of leeches vs quiz only current page I’m on). So I sort of alternate between those approaches. And just using the Item Inspector to read through the list of leeches. ^^
Good luck fighting those leeches! 