I was able to strap the XS650 valve on the back bone right under the front of the seat so that it is pointing its exhaust tube at the oil tank breather tube. I didn't do this because I thought it was mechanically the best decision, but rather that it was better there than not having one at all. I would think that creating any kind of vacuum would work better without a length of rubber hose between the case and the valve. I just didn't want the thing located below my carbs.
I think the best solution is the variety of different proposals that have the valve attached by rigid means to the case. I just haven't gotten their yet. I can't report any negative feedback on the present installation, but any claims to the positive would be purely subjective.
Russ