4 adults this weekend arrived Friday evening, by yesterday afternoon black tank was completely full could see waste water sitting at top of drain.
Depending on your RV. The
bathroom sink usually dumps INTO the black tank.Washing hands and face, brushing teeth etc. WILL make a black tank fill up faster.
I RV solo i.e 1 only one person and by changing just
brushing my teeth and washing hands in the kitchen sink instead of the bathroom sink will net me almost 2 extra days of camping before I have to dump.
Doesn't seem like much but in your case with "4 people"? That's a LOT of water from brushing and washing hands and face etc. in the bathroom sink that is going right down into you black tank.
And if your 4 friends are new to RV'ing my bet is they leave the water on the ENTIRE time they are brushing their teeth just like most do at home. Can't do that in an RV it WILL fill the black in a heartbeat.
Make them all use the kitchen sink! And so that doesn't fill up your gray tank MAKE SURE they do NOT leave the water running when they brush their teeth!! :C