We have seen this topic come up at different times without a resolution. I did not have a choice. I broke the handle on the model 775 and as we have all found out, there are no parts and this model has been discontinued.
I bought the new version 135 which has a much shallower holding tank.
As some of us have found out, this unit does not sit right into the holder that Formula has designed for the 775.
I cut a piece of 3/4 plywood to sit on the ridge of the square base and covered with carpet. Then I used some left over 1/2 in acrylic pieces to fill in the voids. Wood also work.
You will have to cut off about 3-4 inches of the punpout fitting from the 775 so that it will fit into the 135.
When complete, it all looks and operates the same as the 775.
The only thing that sucks is the tank does not hold as much.

Here is how it looks in the boat.

Won't the holding tanks interchange, or is that the part that you broke?

Nice job, by the way...

The bottom part has the handle that pulls out. The tops are interchangable, but you have to buy the whole unit anyway.