These hobby kits are not designed for replenishment, but I'm sure you could process at least 2 batches in the same soup. That is if you don't care about the quality of the 2nd batch as much as you do about the first. There will be differences between the first "pressing" and the subsequent ones.
Originally Posted by Gerald C Koch
You could experiment by replenishing the used developer with some fresh solution. Just realize you can increase the activity of depleted chemicals with replenishment, but you cannot effectively remove the chemicals the film put in there. The 3rd and subsequent batches from the same replenished solution will become even more poluted, and the balance of chemicals becomes very complex.
Since the main reason to process your own film is to obtain best quality and total control, I'd say stick to single shots for the developers.
I used to buy the 20 liter kits (2x10 liter) from Fuji Hunt (NegaColor) and could process 5 rolls of 35mm (or equivalent) in 600ml solution, using the Jobo 1500 tank series on a CPP2. Very economical and no need to replenish the developer. The opened developer concentrates would last at least 2 months.
Testing and experimenting:
I did some qualitative tests on reusing the developer, both with and without replenishing, and concluded that the single shot system gave the highest accutance, and best color, with fewer crossovers. Some may even find the self-processed film to be a bit more contrasty, compared to medium and large lab replenished (and seasoned) tank systems. If contrast is a problem, you can experiment with a slightly diluted developer, say 10%-20% dilution, keeping the time and temperature constant. Reducing time is not wise as 3:15" is shortish already, but you could try.
I've successfully pushed C41 film 2 stops (and even further) by extending the development time. Try to convince your lab to do that for those 2 rolls.
Prewetting film is another variable to introduce. Or the use of extra restrainers.