Originally Posted by bluebird90
... thinking of having just one tank for both. any ideas on size? we will be spending no more than 2 days away from full hookups...
Tankage size depends on your water usage. We have 18 gal tanks (1 black, 1 grey) in the Class C. That would be absolute minimum to me for two (fresh tank is 21 gal). Usually the waste tanks are double (plus a few gallons extra) of your fresh water. I would suggest that you use separate tanks.
When you dump your tanks, it is standard practice to dump your black tank first, then use your grey tank to rinse out remnants of the black tank from the sewer hose when dumping at a dump station. Then you use the water hose at the dump station to run some fresh water down the sewer hose so that it's semi-clean of debris before you store your hose. Please note that this water is POTABLE WATER (drinking water) and do not allow the water hose to touch the sewer hose in any way. You would use this same hose bibb to fill your fresh tanks (which is why you disinfect the hose bibb and use your own hose to fill your fresh tanks... see "how to dump" link below).
When parked in a campground on full hookups, long-termers/full-timers usually leave the grey tank open all the time. But you MUST keep the black tank valves closed or you will get the dreaded "Pyramid of Doom". Some folks will close the grey tank to retain some water shortly before dumping their black tank so that they can rinse out the sewer hose and don't have piles off poo and TP sitting in the sewer hose. Unless you "went" a few hours before dumping your tank, it should have dissolved and you shouldn't have anything but small bit... which can stick up thing. But grey water is pretty stinky, sometimes worse than the black tank. I like to wash dishes or take a shower after dumping the black tank. The water hasn't been sitting getting yukky. But that's my personal preference... and I would forget either to close the grey valves or to open them back.
"how to dump"