Odor when dumping

We replaced the bath fan with the Heng's "super turbo fan" for increased ventilation in the bath area. What we learned is that the fan needs to be OFF before flushing...other wise the fan sucks the air right out of the black tank when the toilet valve opens. When that happens the fan needs to run another 15 mins to clear that smell out!

Make sure you don't have your roof vents going when you dump. Pulls air UP and out of the tanks... It's not just able to come up from the toilet..but also through the bathroom sink and tub drains.

If you are running a hose down the toilet... through the bathroom window...and you have a roof vent cracked or a roof vent fan running... you are gonna pull some nasty air up from the black tank and into the RV for sure.

Then after you dump... make sure you run some water into the sinks and bath tub drains ... enough to get water into the traps.

You may have clogged vent stacks or they may be installed too deeply into the tanks. When either of these cases happen you end up pulling the fluids out of the P-traps when you dump.
During the draining process, you might run water down the drain to keep the traps full or drain the tanks more often before they get full enough to block the vent stacks.