holding tank odors-sour milk!

Mackenzie,

You can use vinegar (a tablespoon) in the head, everytime it smells.

Try using the enzymes that they put in septic tanks that should quickly deplete whatever the odor causing bacteria find so easy to live on.

Check the shower drain. The shower typically drains into the sump and builds a soap scum that sours and really smells. Sorry, wrong forum, you know that. Anyway, clean the sump and disinfect. Will probably get rid of you odor.

Do you have the microphor heads?
If so, behind the flap that opens to allow the waste to fall in a chamber (which is called the hoper,) can get pretty stinking. Every time you flush, it releases the stored gases and will stink up the whole area. What I do is while flushing the head, holding the flush lever, I take a cleaning brush with soapy solution and really try to get in the hopper and knock off all that old waste on the upper sides that has built up. Just dumping chems in there won't do it.
If you don't have the microphor heads and you know every thing is as clean as it can be, than you might have to go tank diving for a good cleaning in there. Chems will only do so well and is usually very temporary becuase of the build up on the upper parts were the chems can't reach.

Mackenzie,
If it's a lingering odor, and not just when you flush, the hoses could be porous and emitting the odor. Rub the hose and smell your hand (or rag) and if it smells, then change the hoses. It's a ****** job, but changing the hoses should help. Good luck.
Capt Tom