I´ve found the easiest method to be using the dong designer. This halves the penis length. Of course if you prefer having only one penis this will make things more troublesome. To solve that you can A visit Dr. Lash and have him remove a single penis, save before you do this in case you have a specific penis you want to keep. You can also B keep multiplying your unwanted D´s to a point where over dosing on condensol removes them. It´s cheaper than dr. Lash. But a whole lot more work. However I rarely find lack of credits to be a problem on Tarkus
If you can´t fit into the dong designer use condensol.
This is usually what I do, in the very least.