Thoughts on a weird/unique way to empty holding tanks.

Pit toilets are not built for RV dumping. Please don't use them for this purpose.

Seems a black tank might fill up that pit toilet pretty quick.

Just drive to that dump station even if not close by and dump

I highly suggest a macerator pump - we've found them very useful and have them on both rigs (Sani-Con on fifth wheel, and FloJet for TC).

It's not something I do often, but I have dumped the tanks into pit toilets a couple times. It's probably frowned upon, and as such, I generally avoid it. If I have no plans to leave a site, it's a long round-trip to an actual dump station, and the vault is very lightly used has lots of visible capacity, are about the only set of circumstances I'll do this.

I guess your method might work, but I've never had much luck with garden hoses and those bayonet caps that have garden hose outlets on them. With a larger hose - or enough actual sewer hose - it would probably work fine.

Now that we don't have black tanks (we have composting toilets), I might dump a five gallon bucket or two of grey water in every couple days. Keeps us from having to move, won't overwhelm the system, and I don't feel as bad about it.

Just how many hoses do you carry?

That might work, but might not. (Bear in mind, of course, that many vault toilets prohibit the draining of cassettes, let alone black tanks!)

The problem will be at the end of the process. Let's assume you have "milked" as much as you can. There will always be a residue at the upstream end of the hose, since the vault is above the level of the black tank valve.

So when you go to remove the hose from the black tank valve, the chances are really good that there will be a little surprise waiting for you.

Let us know what happens -- good luck!