2nd Floor Washer/Waterheater - Overfloor Floor drain tie in.

I have a question about how to attach a floor drain to the trap for a washer.

My plan was to do something similar to this(picture taking from another thread)

My horizontal drain that runs off of the washer discharge is running under(accross) a set of ceiling joists toward the back of the house.

Is there a requirement for vertical and/or horizontal seperation between the floor drain trap and where it ties in to the washer drain?

My thought was to pick it as close to the drain as possible. I will draw it out my thoughts as soon as I can..

But my main question is.. In this drawing what keeps a normally unused floor drain from stinking up the place?

You'd need to install a trap primer. You might be able to do it with a T and an adapter so that when the washing machine was filling, a small amount of water could be run over to the floor drain. How to do that so it looked good is another question. This is a common problem with floor drains. Otherwise, you'd have to dump some water down it periodically. RV antifreeze might not evaporate as fast...check the specs. If you had an overflow, you'd need to replace it, though.