How do I keep the nozzle/hot end clean while printing PETG?

So I'm a bit of newb to 3d printing. Just picked up an Anycubic Vyper, and after looking at my material options, decided to jump right in with PETG (I did buy one spool of PLA, but most of my prints so far have been using PETG). Mostly it's gone pretty well. I've played around with the settings a bit to reduce stringing and such. Generally when I print small figures or toys for the kids it turns out pretty well with maybe a few strings here and there that need to be trimmed off, but mostly things look pretty good. My one remaining problem seems to be printing flat, level surfaces. Whenever printing a fairly large flat surface I get a lot of flaky/feathery strings creating a rough surface and if I'm not watching it and manually trying to pick them out as it prints, they often bunch up in one spot and cause on ugly discolored blotch on the surface. After trying several things, I reasoned that it was just that the nozzle was getting to gummed up with excess filament that was sticking, stringing, and flaking off on the print. So I did a thorough cleaning of the nozzle and started a new print of a flat piece, and watched as the first few layers went down nice and clean. I came back a few hours later after it was done printing the infill, and found it had gotten all gummed up again, and I had the same sorts of problems when it printed the top layer. I'm using a silicone sock on the hot end to try to keep it clean, but that doesn't seem to help much with this issue. Is there anything else I can do to prevent this sort of build-up on the nozzle during printing? Some of my relevant cura settings: Layer Height: .2 mm Print Temp: 220 Build Plate Temp: 70 Print speed: 45 mm/s Initial Fan speed: 0% Fan Speed: 50% Retraction Dist: 7 mm Retraction Speed: 25 mm/s Travel Speed: 150 mm/s

number of issues that i can see.

movement speed way way way too fast.
Set movement speed to the same as the print speed or at best a little faster, and it cuts down on sudden changes of speed which can cause filament 'spikes' and also give the system enough time to perform a retraction.
On a cheap i3 it will also cut down of frame shake and bed wobble.

second:
try 4mm retraction distance 7 is really long. and 50mm/s retraction speed.
That's what i use on my delta, which has a similiar length bowden tube to the vyper. Albeit mine is much better positioned.

looks like you've got double z-axis motors, so best advice: change to a direct drive extruder setup.
The creality bowden setup is hands down the worst setup on the planet. (basically the vyper is an ender 3 clone with double z motors)
The way it goes from a more or less straight tube to a 180degree ubend, is just horrible and causes issues with changing friction levels and filament compression with tpu.

Anyway, back to your petg.
225 is too cool. I know that's what it says on the spool - but it's all lies :-)
I print petg at 245
85c for the build plate
and 50% fan speed after 2nd layer.

Your print speed should be fine.
With your current setup don't try anything over 50mm/s
With direct drive setup you could probably go up to 65 quite easily.
pet-g is a fairly viscous material and can be tricky.

pla is much easier to use, stronger and apart from the heat tolearance - generally a better option than pet-g for most things.

Pet-g is a tricky filament to get right, not sure who recommended it over pla for a beginner - but don't listen to them any more :-)

your print looks pretty good.
One thing to bear in mind - sanding prints is allowed :-)
Pet-g sands like a champ.
so get yourself some foam sanding blocks, don't sweat the surface glitches and after a minute or so with a sanding pad, they disappear :-)
https://www.amazon.com/3M-Sanding-Sp...T%2CB001RB20BS

those and a set of micro files are you best friends:
https://www.amazon.com/Hardened-Strength-Barrette-Crossing-Equaling/dp/B07PPYWSCY/ref=sr_1_8?dchild=1&keywords=micro+files&qid=16349 16358&qsid=141-0333490-1452312&sr=8-8&sres=B07MVW7CLM%2CB0058EDUDC%2CB0058EDUM8%2CB07P PYWSCY%2CB073XYTJ2Q%2CB07TSK23LY%2CB07QYYLH4T%2CB0 95SD9B7R%2CB092D6KFN9%2CB07KH8BG1F%2CB074DQH31X%2C B084WTHG7J%2CB0045L7Z1W%2CB07RQLBN9H%2CB07VNJWWZM% 2CB00002N5JT%2CB07WF6KZBX%2CB087FXBL69%2CB081DXD5K 5%2CB07FS649BD&srpt=HARDWARE_HANDLE

Hey, thanks for the tips, I'll give them a try, although its curious that almost all of your suggestions seem to be the exact opposite of what I've read elsewhere in tips to reduce stringing with PETG. Low print temp, high retraction distance, low retraction speed, high travel speed. All of these were done to reduce stinging, and I actually managed to print a small perfectly clean stringing test model with these settings.

No one recommended I start with PETG. I just read up on it, and it seemed like if I could figure out the right settings to get it to print well, the the extra heat resistance would be nice. I'm sure most stuff I print would be just fine with PLA, but I like not having to worry about is this something that might at some point be left out in the sun on a hot summer day, or something. Plus, PETG is a lot more easily recycled, so that's also a plus. And most of my prints have turned out pretty well, just working out a few more kinks here and there.

Regarding the direct-drive extruder, I may consider that down the road a bit, but I want to get a bit more of a feel for the capabilities of what I have before making any major upgrades.

About the sanding bit, yes I'm aware I can do a little work to smooth it out. I'm less concerned about the somewhat rough finish then i am about occasional large clumps of filament strings getting stuck in one spot and leading to discolored "burn" marks here and there, or on occasion having the nozzle bump into the clumps and knock the model loose from the print bed. I've had a few prints fail that way.

One other thing I forgot to mention is Z-offset. I tried setting it at .1 mm which seemed to help a little. I wasn't sure I should go much higher than that initially, but after printing a couple of benchys and barely being able to make out the letters on the bottom, I decided to bump it up to .2 mm. Haven't tried another big flat print since I made that change, but I'm hoping that will help a bit too.

yeah well my advice is pretty much based on what works for me.
As well as taking the viscosity and flow rate of the material in mind.

pet-g, even at high temps, does not become the fast flowing liquid that pla does.
printing it cooler will tend to worse layer adhesion and a thicker flow that is more prone to stringing.

The really long retractions will increase blobbing. As you're esssentially removing it from the hot zone and then pushing it back in every time. That creates 'waves' in the material flow.
Likewise long slow retractions are going to make the flow uneven and create thick and thin print extrusion.

Shorter retractions are generally better if you can manage them.
The less semi molten plastic you're pushing and pulling the better.
And with most rigid filaments, the faster and shorter you can do a retraction - the cleaner the print will generally be.

I watch very few youtubers and much of what I do see, tends to be complete nonsense.

3d printing, is as much an art as a science. And what works for one person, won't necessarily work for someone else.

Also the pet-g you are using could well have a very different chemical composition to the stuff (creality white) that I've been using.

So anything anyone says to you, can only be a guide, at best.