Longest time before emptying black tank?

As stated, just use plenty of water if solids are present, drop in a packet of tank treatment if you are so inclined and don't worry about it.

But I gotta ask...........When it DOES come time to dump the black tank, WHERE AND HOW are you going to do that ??

And does your rig really have 3 water tanks that are each over 50 gallons ?? (black, grey and fresh) ??

I feel certain the OP has checked his zoning and land management sources about this, so this shouldn't be an issue with this discussion.

About the subject, how long in the tank? If you have the ability to dump the tank freely, then why not? If you freely have water, then add a few more gallons of water every time you are ready to leave, and then dump it. Pour some Dawn Dishwashing Liquid, some Tide Laundry soap, or any laundry, dishwashing product down the toilet, add another gallon or 2 of water to the tank so the bottom of the tank remains wet (and soapy) and leave.

Leaving "contents" in the black tank will not hurt the tank in any way. The problem you will experience once the "contents" ripen up over time, is ... every time you push the pedal on the toilet, you're going to get a fantastic whiff of a smell of "you know what." (Been there, done that, it's not pleasant). The odor can permeate the entire camper in just a flash when you push that pedal! Not pleasant at all. Keep the tank clean, and good smelling, and you won't ever have that problem.

I have left black tank over several months.. and as long as I ensured plenty of water, no issues.. Used TT just before Thanksgiving and ran into issues that I didn't dump. Fast forward to early March before I got trailer out.. used it that weekend and then dumped. Just ensured I put lots of water in it. Also I kept a jug of water in the bathroom, and periodically poured water into bowl. it seems the seal is either not completely watertight or water in bowl would evaporate.. keeping water in bowl over seal seems to be key to keeping smell out.

FireGuard wrote:
I'm posting here as I figure most full timers or boondockers have 5th wheels.
I have a 21' Toyhauler with 58 gal holding tanks and keep it on my 5 acre lot as I develop and build.
I have a water supply and can dump the Grey on the ground but I only spend 1-2 nights a week in it and only use the toilet in the morning and once or twice at night as I water the trees when I'm outside working.
I could probably go a couple of months before filling it but curious if there is a point where it gets nasty.
I haven't noticed and smell or issues so I'll wait until I take it camping and dump before bringing it back up.
Thanks.

While normal RVing in various sites and RV parks, I can go 8-10 days before dumping. My concern in your situation is the possibility of developing the dreaded solid poop pyramid and then be faced with not being able to dump. RV toilets/tanks need sufficient water to avoid having your tank plug up. What do your black tank gauges indicate. you might consider having your tank pumped out.

ACZL wrote:
Will OP's water evaporate in the black tank over the course of time?

As OP states using it everyday more than once probably not.

Will OP's water evaporate in the black tank over the course of time?

It's just a plastic tank filling up with water,urine,dissolving paper and poop. Use waste holing tank digester tablets or liquids to control smells. The rv toilet shuts inside and has a vent through the roof and should be fine, even over months of use.

As long as water to stuff ratio remains high then no issues.

Liquids are the key