I used the same kind of toilets in a RV, going camping with wife and kids.
I drained it only after 4 days, as per the rental agency advice.
You take the tank with you, walk 50 metres to the toilet of the gas station, and drain it over the toilet. It smells nothing at all...
It's not my money, but around here it's about 80/100€ and take some time.
Would be happy to avoid it in summer if necessary.