If you can get it to fit on my Kacher then you've got a customer waiting!

 

I regularly just use a hosepipe and spray up into the arches to loosen off any mud and crap, and give the underside a good wash in mains water to get dried-on salt off etc.

I also have an angled attachment that does fit my Karcher pressure washer that came from the middle aisle of LIDL for about £11. This is fantastic for getting a lot of crap out of the arches and giving the underside a very thorough blast, however care must be taken as it is very powerful. Looking online, there are other angled lances etc. that fit various makes of pressure washer.

Karcher did also make a chassis cleaner, which looks essentially like a patio cleaner upside down on wheels. They no longer sell them, but they do come up on ebay etc. but are quite sought after so can be £50-80.

I have found that the main areas that really accumulate dirt are the arches- these are easily washed out regularly with a hosepipe without jacking the car but if you've never done it there will be solid chunks of mud that need removing either manually or with more powerful washing. Once you've got the worst off regular clean water washing all the salt and loose dirt away works pretty well. I also take care to hose water behind the sill covers to ensure no salt-water is trapped there, however these have been off and cleaned out properly in the past so this is also maintenance.

Basically, I think if you take the time to get all of the built-up dirt off, regular light cleaning so that salty water and mud never stays on for extended periods and nothing can build up again is better than infrequent but harsh cleaning.

You can buy a washing additive from autoglym that neutralises salt as well- I have never tried this but have been meaning to. You can also buy similar in bulk from agricultural suppliers for machinery but I have no idea how harsh it is so wouldn't personally recommend it!

 

Some good advice here and brings back some memories for me.
When I was a teenager, I spent a summer working with a valeting company. Once you'd finished a car, the boss would run his fingers along the inside of the arches and they had to be spotless otherwise he'd make you start all over again; that's a 5-6 hour job! A tough lesson but now my arches are the first thing I clean! lol.

 

Just had a look and there's loads on Amazon!

 

Another thing that's pretty straightforward and a very fast way of giving the underside a good clean, particularly the problem areas at the rear-

Trolley jack under the rear diff
Snow foam the rear underside and arches
Wait a bit
Wash it off

I normally let it back down rather than hold it up on the diff for ages while the snow foam works as I don't want to hold the bushes out of position- it takes seconds to jack the car on the diff as the rear as access is so easy. Sometimes if I'm doing a quick maintenance wash I snow foam the underside, let it down and do the rest of my wash quickly, then jack it back up and wash the foam off.

 

I’m not sure about you enthusiasts but the sun is out, it’s still cold now but when it’s 25 degrees odd I can’t wait for the car shows, greasy burgers and burnt rubber smell around July / august time. Cannot EFFIN wait 😁👍

 

What’s the score with Santa pod? Just watching YouTube and instead of it being a race against the car next to you, does your time only start when you move? Some cars get quicker times when they take there time if you get me and don’t necessarily race against the car next to them. Can’t wait to get there this year