Except the side-arm connection on a dishwasher sink pipe, is way smaller than than the drain
But the washing machine hose on these small machines is about the same size as the dishwasher tailpiece. It's not much of a restriction at all compared to the line that hooks into it. Again, we're talking about less water than a dishwasher uses.
I have not seen and can't seem to find data on flow rates for small washers. But when I see that Bosch recommends a dishwasher tailpiece as an option, I'd think that it would at least usually work. (IE: the pump isn't that fast.) They could very easily say that a standpipe is recommended over any other option, etc. But instead leave several options.
I would assume also that the flow rate would be low enough for this to work as these smaller machines aren't really competing on cycle time, etc of the bigger machines. So they don't need to drain as fast as possible. (In fact, a complaint some have about the smaller machines is long cycle times.)
Did a little research. Found that for normal to large size washing machines, the fastest pumpers have flow rates of 17-21 GPM!
According to what I've found, a 2" trap fixture could be up to 22 GPM. Which is what I'm assuming the washer manufacturers are working off of. (They assume a perfect system for the highest flow washers, I guess.)
So I'm assuming that chart is then correct, since I haven't heard stories around here of properly plumbed 2" washer lines overflowing.
So, 1 1/2" drain should be able to handle 15 GPM. If that is true, then the 4.4 gallon discharge from the Bosch I'm looking at would need to take at least 18 seconds to not back up into the sink. I don't own it yet, so I don't know if that's true or not.
Either way, clothes washers
used to only need a 1.5" line for full sized units, correct? In fact, in WI (I know, we're not a good example at all) it's still code for a 1.5" standpipe for a clothes washer. And clothes washers used to hold a LOT more water than the 4.4 gallons I'm talking about draining through a 1.5" drain.
Will be interesting to see if codes do change to reflect the increasing usage of low water usage machines like this as Redwood mentioned.