I currently have a 2 bedroom, 1 bath house, built in the '50s with a garage that has been converted to a workshop. There is plumbing for a washer-dryer in the workshop area. I want to convert the workshop into a bedroom and add a bathroom, but because the workshop area is on a slab (the rest of the house is pier and beam), I'm not sure if it's feasible or affordable.

I will hire an expert to do the labor, but am concerned about cost and, as I said before, possibility.

I have done some research on the toilets that flush up... is this the only/best way to make this work, and can the same be done for a shower?

You are more than likely way ahead of me on this, but the first thing you need to concern yourself with are the permits and designs. Depending on the regulatory agency in your area, you will need to pull a permit after getting your plans signed off on.

To answer your question about the plumbing, yes, you can put in a Shower, Sink and toilet. They make pumps that pull the waste water out and delivers it to your septic system.

Example: Saniflo, "Add a bathroom anywhere without breaking the floor or the bank":
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Here is a great demonstration video from "This Old House", showing you how the unit is installed:
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Is the garage part of the house or free standing structure ? Back to you. Milo

You have options here,
1. You can dig up the washer line to the sewer and increase to 4" and break the slab and install your bathroom group. **OR**
2. If you want the extra expense of installing a Saniflo unit you could connect to the 2" washer drain line.
Your choice! What's it going to be? Door #1 or door#2? Good luck, Tom

I wonder if the OP has already fixed this problem since the OP was back in 2007.

I wonder if the OP has already fixed this problem since the OP was back in 2007.How right you are but look at post#2 and you'll see who dug it up. I said I'd answer dead threads just as though they were current. Do I fell silly? You guess. Cheers, Tom