I have a 27' Wildwood travel trailer that we take camping to Provincial Parks which do not have sewer hookups. You need to either haul the whole trailer to the dump site or get a portable tank.
Black and grey water hits capacity about day 3 as we have family members with medical issues that lead to a preference for not using public facilities.
Here is the problem...the clean-out valve is so low to the ground that the bayonnet fitting attachment on the portable tank is 4-6" higher than the dump valve on the trailer. Which means that effluent has to travel uphill to get in the tank.
Raising the trailer on levelling blocks has not been a viable option. Any of you pros have an idea or face the same problem?

We use a motorhome. But the last one we used had a tiny gray water tank so I feel your pain in a distant sort of way.

You could get a macerator pump that attaches to the rv. Macerator attaches to rv and the outline is a garden hose. Macerator pump into waste tank than go to dump site. Some folks even use the macerator and pump directly into a toilet. Put a clear fitting before macerator pump to be able to see what's going on at pump inlet. Run a little grey water first to make sure pump is working then go to back to normal black and grey water dump procedure.

I think this has promise, going to do a bit more research