The most hygienic way of draining the used water from your washing machine is to hook up a sink and washing machine trap under your kitchen sink. Some people opt for and open-ended standpipe connected to their drainage system, but this is more expensive and runs the risk of dirty water leaking into your home if your drainage system becomes blocked. Once you've got the necessary equipment, installing a double trap in your kitchen is a straightforward task.
Unscrew the compression fitting connecting the waste trap to the bottom of the sink. Make sure the sink is empty. Then, measure the threaded connector. Take a picture of the connector, too. This will be useful when sourcing a new double trap from a plumbing supplier.
Measure the outlet at the end of the washing machine's drainage pipe. Take a picture of that, as well.
Visit a local plumbing supplier and ask for a sink and washing machine double trap. Give the plumbing supplier the dimensions of your current trap and the type of outlet at the end of your washing machine's drainage pipe. Show the pictures to illustrate what you need. Most newer sinks and washing machines have uniform connectors, but there's a chance that yours may be unusual. The plumbing supplier should be able to find the correct trap unit based on the information you provide.
Unscrew and remove the existing trap from under the sink. You may want to place some old towels below the trap when you remove it as water residue is likely to leak out.
Fit the new trap under the sink by pushing the top pipe into the sink outlet and connecting the bottom pipe to the outlet connected to the main drainage system. Then, screw the connectors into place.
Push the washing machine's drainage pipe onto the second intake on the trap and secure with a jubilee clip.
Secure the drainage pipe above the level of the sink overflow with the wall brackets to prevent back-siphonage.