UNDERCARRIAGE CLEANING

Possibly with a pressure washer with a right angle wand or 90 degree adaptor. But be careful of using too aggressive of a pressure nozzle to avoid damaging rubber parts.

 

Assuming you haven't access to ramps, jack stands or a lift I guess a power washer would work. If you can make a curved spray arm that you can direct under the car this might be a good option. I don't like spraying the underside myself because it forces water into crevices and areas I cannot wipe dry or clean. If you can somehow get the car to where you can get underneath the undercarriage use a product called Boeshield T-9 on any metal parts and Adam's undercarriage spray on the rest. Boeshield lays on a protective coating that lasts for up to a year and prevents rust or corrosion and leaves a OEM matte finish.

https://boeshield.com/automotive-motorcycle/