Ideally you should have a separate foam hose for each different chemical, if you use the same hose for each product (without a rinse step) you may end up getting a reaction between the two chemicals.

A good example of this would be using a chlorinated foam detergent, then a quat sanitiser in the hose straight after. These two chemicals are incompatible as one is cationic and the other anionic, which lead to deposits occuring in the foam hoses. These are a precipitate formed over time and are virtually insoluble so quite difficult to remove.
In the above situation you may have to replace the hoses and you would probably want to get a second hose for each line to stop this potentially happening again.
If you would prefer to stick with a single hose, it would be best to add a rinse step between different product uses. You would be best to run water through for 1-2 minutes before moving to a new chemical.

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