you're right about the shower draining into the gray tank. that's how it's been in RVs too.
this is a recent development in RVs. i think for smaller trailers with tank size limitations, there have been complaints at how limited the gray tank capacity is without any similar complaints about the black tank capacity.
so, i think that it's a way for smaller trailers to go longer without their gray tank filling up and since the shower is next to the toilet, location makes it easy.
maybe a FR rep can answer this.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC