Originally all of them drained to the ground (it is only water and a bit of soap), but this was changed with the newest models... or so I read. The bathroom water goes into the main black/gray tank.
This is one of the ways that they kept the labor to build one of these to one hour. LOL As Jim Hammill bragged on FB...
Good to see that you found the FB page. You might also want to join the Hymer Aktiv Owners group which has a number of owners who are better at the tech in these rigs than most of the techs at EGHNA were. They organize meet-ups around North America to help get the tech end of these vans functioning properly and safely. When you are orphans, you have to do a lot of the work yourself. :C
Luckily you can do most of it, but these lithium/balmar/UHG/solar systems require a few tweaks.
Mumkin
2021 Promaster 1500 188wb conversion
2019 Roadtrek Simplicity SRT (half Zion/half Simplicity)
2015 Roadtrek 170
2011 LTV Libero
2004 GWV Classic Supreme