try buying a baby toothbrush... it's super soft but will scrub the dirt out of the cracks in the sole.
I don't use such a extensive methode to cure bumblefoot. I soak in ALOT of epsom salt, little WARM water for 10-15 minutes two or three times a day... wash it well with the brush... take tweezers and gently pull the scab up around it's perimeter... often by the second or third soak it comes right out (the whole "plug"). Once that happens I clean it, soak it, clean it again (anti-bacterial soap) THEN put the triple antibiotic IN the hole (tehre usuaully will be a hole). Put her (let's say it 's a hen) in quarentine... she is contagious... bumblefoot is Staph... and also because she needs to be in a controlled enviorment. I use towels for bedding... washed everyday... twice a day (this usually only lasts a week). I do not bandage up the foot... i do not take a blade of any sort to her foot. Just epsom salt, a baby brush, antibacterial soap, and triple strenth antibiotic cream.... and clean towels. It's a infection... a staph infection... and I treat it as such. It's up to you to give anti-biotics or not... some are against them in poultry. It's your bird, your choice.
I hope I didn't confuse you... but wanted to tell you what has worked for me time and time again. I'm not a vet (probrably no one else on BYC either... not that I have ever come accross at least)... but this is what has worked for me.