[Grammar] Singular or Plural?

[Snappy]

I have two questions.

1. Does the following sentence make sense?

"Do not attempt to clean the product in a dish washing machine or dish dryer or use the product in a microwave oven."

2. Do I have to say, " in dish washing machines or dish dryers or use the product in microwave ovens"?
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[mmasny]

Why should you use plural forms here? The warning's addressee has probably just one dish washing machine and just one microwave oven. There is some logic of course in using the plural form too, but it sounds worse to me. I feel the plural number unnecessary in this sentence (this is just a feeling - taking this logically, someone could ask why isn't singular unnecessary either).

I am not a teacher and not a native speaker, so you'd better wait for other users' replies.