Beware of using Milton. It has many uses when cleaning but do not spill or use neat. Read the instructions and make sure you dilute to the correct level.
Advice given so far is sound.
I would add that some motorhomers, like me, have a SOG system installed so do not use any chemicals. Problem solved permanently!
A SOG does not save money because the cost is likely to be greater than the cost of the chemicals. However, it is environmentally better. Like a domestic toilet, it relies solely on clean water but has a small motor that removes odours through a charcoal filter. Nature takes care of decomposing the waste but when emptying, the waste does tend to smell awful. Solution to that is to empty the cassette regularly.