Thanks for letting us know because this could be an issue in other types of rigs as well.
Unfortunately, there are many times when what sounds good in theory isn't always the right solution when applied in the real world.
In this case, I would have never believed the bathroom sink could provide enough water flow to wash solids down to the deep end of the tank. You would have to fill the sink to the top and then pull the stopper to have even a minor effect given the size of the typical bathroom sink.
I have a Class Outlaw 29H and the bathroom sink is also plumbed to the black tank. The only reason to me you want to plumb it that way is to make sure you are adding enough liquid to flush the solids out when you pull the valve.
__________________
|