Dirty water in toilet bowl after sitting

Probably drainage from your (dirty smelly) fresh tank and water lines.

Not related to the OP's question, but I would suggest keeping a little water in the toilet bowl to help prevent the seals from drying out.....

The fresh water tank is empty and the valve to the toilet is closed.

Could some amount of sewer water still be in the tank and somehow be coming up into the toilet from below?

spuyear wrote:
The fresh water tank is empty and the valve to the toilet is closed.

Could some amount of sewer water still be in the tank and somehow be coming up into the toilet from below?

No. That would defy gravity.

Water can only get into the bowl through the toilet valve (or someone peeing) ... maybe the valve is leaking and needs replacing? Since the water supply to the toilet come from your FW tank any water should be clean ... if it's dirty then you should sanitize your FW system ... lots of threads on that subject ... use the forum search feature.

Hope this helps.

Toilet has a vacuum breaker (small container with hole/flapper at top)
After toilet is flushed the flapper opens an allows the water in vacuum breaker to drain down into bowl

As noted:
Should leave water in toilet bowel so seal doesn't dry out and the water is a Vapor Barrier so black tank odor doesn't come back up thru bowel

Should also put 4-5 gallons of water BACK into black & grey tank so bottom stays wet...keeps stuff from drying out/sticking/stinking
YES...there is some stuff left behind even when flushed

RV A/F (the pink stuff) with propylene glycol makes a good winterizing bowl seal when not in use. It won't evaporate like water, and usually provides some degree of lubrication.

You left the ceiling vent open and it’s been raining?:)

F1bNorm wrote:
You left the ceiling vent open and it’s been raining?:)

Good one. :B

I had the same thing happen to my RV after a couple weeks of storage -- it only happened once and I never found the cause.

I use TankTechsRx probiotic tank treatment (it has live bacterial cultures), so I'm blaming it on not flushing long enough to clear out the TankTechsRX from the toilet bowl, so some of the bacteria grew in the bowl.

Not sure if that was really the cause, but I've been flushing more thoroughly and usually spray some toilet bowl cleaner in the bowl before the final flush after parking, and I haven't had it happen again.