Hey there,
I'm a bit of a beginner at slap, I'm learning can't stop by RHCP. Though I
think my action may be to high for slapping... What's a suitable height?

My treble side is about 5mm off the 12th fret.
The bass side is around 5mm off the 12th fret measuring from the bottom
of the string, about 8mm if you measure from the top.
To high? Or should be okay? It might just be that I suck haha.

Also I'm hitting the string with the knuckle bit of my thumb, is that the
correct spot? and around how far up the neck should my thumb hit?
My slaps don't sound great and I'm trying to figure out how to get that
great sound that other people can get.

usually, the a bit higher action is good for slap and pop..but there is a limit and your's might be TOO high or just right. Just practice it the way you feel comfortable and gradually your speed will get better..don't worry about where you're thumb should be exactly.
Okay thanks, Do you have any tips to get that slap sorta tone?
Mine sounds kinda... Umm trashy haha. It's almost certainly
my technique I think, but could it have anything to do with the
fact my bass just isn't cut out for slapping? It's a squire P-bass.
I have been able to slap on almost any bass, and while I'm not that good at it, different basses definitely produce different tones.

Take for example, My old Ibanez GSR190 and my current Cort Curbow 4, The Ibanez produced a more thrashy sound, it had some grunt to it, but the cort produces a rounder slap which I preferred.

It could simply just be the bass. And if you're wondering where to slap, do whatever feels comfortable. There is no right way to slap, just a general outline of what to do. I slap with the tip of my thumb, I know people that slap almost with their palms. It's simply your technique that you have to adjust to.
Quote by srvguitarrulez
I heard someone say that Fall Out Boy had amazing guitarwork. But, it was a 13 year old girl, so it didn't matter.
Something I did when I first started slapping was lowering my neck pickup some, which gave me more room under the string to work with, and also produced generally a little more treble-y sound since my bridge pickup was now the closest one to the strings. So maybe try that.
I learned to slap years ago on a squire P, and the action was awful on it.
You'll just appreciate it alot more when you buy a better instrument.

Quote by TimeIsTheEnemy

My treble side...
The bass side...

Lower and higher strings don't determine treble or bass, your EQ does that.
Just refer to it as your top end or low end, or the string name.
Okay thanks a ton. Not really relevant, but once I have a new job I plan on
getting a new bass, and amp.. Maybe a musicman stingray if I can afford it
Hold down each string at your highest fret and make sure there is plenty of space between the string and your pickups. I also slap with my knuckle and learned a p bass. I used to have terrible slap sound untill i lowered my action which was terrible, and lowered my pickups. Now it sound pretty nice for a peice of **** bass.