Our camper originally had a high pressure city water hookup plus a pump facet from a large water tank under the dinette seat. The sink itself just drained right onto the ground which is generally frowned upon in modern campsites.
To simplify things we decided to use two 5 gallon Jerry cans directly under the sink. For the drain side, we used a 1-1/2" plastic RV drain and hose. This is intended to be mounted to the outside of the camper and hooked to a hose, but we wanted to have the waste tank inside for easy setup, so we needed to trim the waste flange to fit our jug lids.
A little trimming with tin snips and some sanding and it fits well.
We took apart the cheap plastic rocket pump only to find that 3 of the corner standoffs were broken. What a piece of crap! A new pump runs $30 and gets terrible reviews, with about half of them seeming to leak, so we did what we always do...
...We improvised! With the trailer, hidden in a drawer, was an old (original?) hand pump made of solid cast metal. The chrome even looked better than the cheap plastic chrome of the new replacement.
The only problem was the gasket was old, loose and fell off the piston when pumped. We tried to take the gasket off the plastic pump, but it was hard plastic and wouldn't come off, so we decided to graft the plastic piston onto the old metal pump mechanism.
As the old pump cylinder was a little narrower, we had to trim and sand the piston plastic again. In our first test, the pump worked perfectly. We sealed it up with silicone and will install in a few days.