Access to greywater can be lost when pipes enter a concrete slab foundation. If your house is on a concrete foundation you still have some greywater options.

1. Use the greywater from your washing machine, as you can access it with out needing to alter the plumbing.
2. Use greywater from sinks. It is often possible to attach a 3-way valve to the trap arm of your sink, enabling you to send the pipe outside before it enters the cement foundation. This breaks some of the conventions of plumbing, but is fine to do in practice. The greywater side is not connected to the sewer, so no trap or vent is needed (all drains have traps on them that have standing water to prevent sewer gasses from entering the building.
3. Elevate a tub or shower to access the plumbing.
4. If there is a second floor, use the greywater generated from there.