? About emptying camper tanks into external holding tank

That macerator pump might be exactly what I should get, thanks.
I dont completely see how it works and why I'd need an additional hose though.
And yea, I'm planning to put my external holding tank in the back of my truck.
And I could dig out an area for my tank but it's not ideal cause to get my camper back out I don't want to get it stuck in the hole.
And to Heymon, that's a good idea but it just isn't ideal.