If there is one grey tank there will likely be one drain that your sewer hose hooks to doing the work for both the black and grey tanks, but a valve for each tank. If there are two grey tanks there will be a separate drain for the second grey tank, usually the galley tank.
2017 Coachmen Catalina 283RKS
2018 Ford F250 Super Duty 6.2l CCSB
2010 Jayflight 28BHS (sold)