ARGH! Black tank odor inside camper but figured it out

Another smell trick is when the smell is actually coming from the grey tank. On some campers, like mine, the vent cap is under the kitchen sink. That cap had rattled loose on mine and the smell of decay was filling my camper. I first tried masking it with treatment to the grey tank but when I found the loose vent cap and tightened it, all was well again.