For me the smell is one factor, the other major factor is the convenience of reducing the possability of cross contamination. I wear disposable gloves when I dump the tanks. I then place the hose back in the carrier tube. Remove and dispose gloves, wash hands and drive off.
Many times I've been behind someone at the dump station, or witnesses a neighbor drop a container on the ground near the discharge hose and remove the cover and trow it on the ground. Remove hose, wrestle the hose back in the container and close the lid. They never wash off the container before placing it back in storage compartment. I'm not a germaphobe but I don’t like playing the odds with that scenario.
To each their own.
2012 Laredo 303 TG
2010 F250 LT Super Cab, long bed, 4X4, 6.4 Turbo Diesel