How come we don’t use dishwasher for milk and meat
I saw a tshuva in Rav Moshe that it’s permitted
There are numerous problems with using a dishwasher for both milk and meat.
The walls absorb taste of the first type and then get washed with hot water of the second type.
The racks get soiled from residue of the milk and the meat.
The filter contains residue of the meat and the milk. Sometimes the filter, which contains both the milk and meat contains the heating element.
Even according to R’ Moshe one needs separate racks for milk and meat, and preferable the dishwasher should be run on an empty cycle between the two.
Regarding the issue of the filter, it is possible that when R’ Moshe wrote the teshuva the dishwashers didn’t have the filter issue.
The laws of Kashrus pg.258-262.