I hate to admit it but we had the reverse experience last trip. After four days boon docking we still had lots of water in the freshwater tank so I didn't even worry about the black tank filling up. No dump site nearby. One more day. Noticed a bit of sewer smell outside on the driver.s side, thought it might be the neighbour but did put some odour control stuff in the toilet in case it was us. Headed for home. After an hour of driving and a couple more flushes, we stopped at an art gallery. I did the walk around and noticed the much stronger smell was with us . . . and a brown streak on the side downwind from the blank tank flush inlet. Definitely time for a dump!!