I dont know if this would work for the average weekend camper unless you have a Macerator. From what I've learned from talking to the weekend warrior, is they go away fro a few days, clean out their tank before driving home at the camp ground and let it sit empty till the next time they are going to be traveling.
One thing we've been doing between tank flushings is, after we have throughly emptied out both the black and grey tanks, this involves using the factory installed black tank flusher to fill the tank up numerous times with clean water untill the water comes out clear with no debris. I then fill the black tank up with clean water till it reads 1/4 full and run some clean water into the grey tank and leave it there. While we drive from one spot to the next, I let the clean water slosh around in the tanks cleaning anything off the sensors or anything that might have stayed behind during the original flushing session. Once we get to the next campground, or dump station, I just let them drain out before adding anything to it.
They are usually clear of debris and this has so far kept both tank sensors working fine. Now if you were leaving the campground heading home, you might be able to just empty your grey tank out into the yard, since you know it's just clean water that has been sloshing around in there. Unless you ahve a macerator, I wouldnt empty your black tank out in the yard, as the first few times, you might be surprised at how much stuff was left behind.
If you dont have a tank flush kit installed, buy one or use one of the wands that can be inserted through the inside of the coach through the toilet. You'll be amazed at how much sludge is left in the tanks with out this procedure.