My 12-year-old cat has inoperable sarcomas on her back. This is the best everyday care routine I've discovered so far:
I wash the area using a spray bottle containing sterile saline (1/2 tsp salt boiled in 1 cup of water) and blot with kleenex, gently probing into the cracks where the foul leakage comes out. When the area is clean I spray with strong turmeric tea (boil water, turn off heat, add turmeric and a little black pepper, steep half an hour or so, filter out solids). I keep the spray bottles in the refrigerator. The tumors are hot so I think the cold spray is good. She is more energetic immediately after the treatment and the tumors are leaking less. To keep her from licking the part she can reach I loop an elastic bandage behind her front legs and tuck paper towels under it to cover her back. I tried castor oil poultices but her energy was down after the treatment and it gummed up her fur. The gummy texture made it hard to keep the area clean. What goes on the skin gets into the bloodstream and I'm not sure castor oil is mild enough. I don't worry about the turmeric. This routine is working well enough for maintenance. I am still trying to find the best way to actually shrink the tumors.